Notes · XB Field Notes

A maintenance timer should leave its last result visible

Tue, 04 Aug 2026 00:00:00 +0000

Cron-like syntax is not the whole contract for a maintenance task. The command needs a clear service identity, a bounded runtime, and evidence that distinguishes “not scheduled” from “ran and failed”. A systemd timer and oneshot service keep those concerns separate.

Define the work as a service

Use an explicit user and absolute command path:

# /etc/systemd/system/site-check.service
[Unit]
Description=Read-only public site check

[Service]
Type=oneshot
User=sitecheck
ExecStart=/usr/local/bin/check-public-site
TimeoutStartSec=2min

TimeoutStartSec prevents a network or subprocess wait from occupying the schedule indefinitely. The helper should return non-zero when its contract fails and must not modify the service it checks.

Schedule the service

# /etc/systemd/system/site-check.timer
[Unit]
Description=Run the public site check every hour

[Timer]
OnCalendar=hourly
Persistent=true
RandomizedDelaySec=5min
Unit=site-check.service

[Install]
WantedBy=timers.target

Persistent=true can run a missed calendar event after the machine returns. RandomizedDelaySec spreads routine work across a window; it is not appropriate when the task must run at an exact instant.

Validate before enabling

Inspect the calendar expression, then start the service manually:

systemd-analyze calendar hourly
systemctl start site-check.service
systemctl status site-check.service
journalctl -u site-check.service -n 50 --no-pager

Enable the timer only after the service succeeds with the intended user, environment, paths, and network access:

systemctl enable --now site-check.timer
systemctl list-timers site-check.timer

Alert on the service result

The timer firing is not success. Monitor the oneshot service’s exit status or journal result. Keep stdout concise and send detailed artifacts to a bounded path if they are needed for debugging.

Sources

systemd.timer(5), calendar timers, persistence, and delay behavior, checked 2026-08-04.
systemd.time(7), calendar expression syntax, checked 2026-08-04.
systemd.service, oneshot service semantics, checked 2026-08-04.

Restart policies need a rate limit

Mon, 03 Aug 2026 00:00:00 +0000

Automatic restart is useful for a long-running service, but an unbounded loop can turn a clear failure into a noisy one. The unit should describe both the normal process lifecycle and the amount of recovery that is acceptable.

Track setup failures

For a long-running process, Type=exec makes failures to execute the configured program visible during start-up rather than treating a fork as success. Pair it with an explicit ExecStart and the least-privileged User that can perform the work.

[Service]
Type=exec
User=site
ExecStart=/srv/site/bin/server
Restart=on-failure
RestartSec=5s

Restart=on-failure is a recovery policy, not a health check. If the process stays alive while serving bad responses, systemd will not know that the site is broken; an external smoke test still has a job.

Bound the loop

Systemd applies start-rate limiting through StartLimitIntervalSec= and StartLimitBurst=. Choose values that allow a short transient outage but stop a crash loop from consuming the host’s resources. When the limit is hit, the journal should contain the evidence needed to distinguish “restarted successfully” from “gave up after repeated failure”.

After changing a unit, verify the loaded configuration and inspect recent logs:

systemctl daemon-reload
systemctl restart example.service
systemctl status --no-pager example.service
journalctl -u example.service -n 80 --no-pager

Do not use a restart policy to conceal missing files, invalid permissions, or a bad environment. Fix the first failure, then test the recovery path.

Sources

systemd.service, service type, restart, and start-rate limiter, checked 2026-08-03.
systemd.unit, common unit sections and drop-in semantics, checked 2026-08-03.

A release checklist for a static site

Thu, 30 Jul 2026 00:00:00 +0000

A static site is simple to publish, but simplicity does not remove the need for a release check. The useful checks are small enough to run on every release and specific enough to fail for a real reason.

Build a clean artifact

Use a pinned generator version and build into a disposable output directory:

hugo version
hugo --gc --minify --destination public

The exact command depends on the project, but the important property is that the output is reproducible from the tracked source. Do not edit generated HTML by hand after the build.

Check the artifact, not only the source

Inspect the generated tree and verify that expected entry points exist:

test -s public/index.html
test -s public/404.html
test -s public/robots.txt
test -s public/sitemap.xml
find public -type f -print | sort

Then search for accidental placeholders, local paths, and development-only hosts:

rg -n 'localhost|127\.0\.0\.1|TODO|example\.com|/Users/' public --glob '!notes/a-release-checklist-for-a-static-site/**'

An intentional example in an article should be clearly fenced as an example. A host name or private path in a link is usually a release mistake.

Exercise the public routes

Serve the artifact locally and request the paths a visitor can reach:

hugo server --bind 127.0.0.1 --port 1313 --disableFastRender
curl -I http://127.0.0.1:1313/
curl -I http://127.0.0.1:1313/notes/
curl -I http://127.0.0.1:1313/resources/
curl -I http://127.0.0.1:1313/missing-page/

Confirm that the 404 route returns a 404 status in the production server. A pretty error page with a 200 status still breaks monitoring and caches.

Record the result

Keep the source commit, generator version, and checksum of each downloadable resource in the release record. This makes it possible to compare a live file with the source that produced it without relying on memory.

The downloadable version of this checklist is in the Resources section.

Sources

Hugo command reference, generator flags for a clean production build, checked 2026-07-30.
curl manual, HTTP verification and header inspection options, checked 2026-07-30.
Static-site release checklist, downloadable companion resource.

SSH host keys are part of the deployment record

Tue, 28 Jul 2026 00:00:00 +0000

An SSH private key authenticates a client; it does not tell the client which server it reached. The server’s host key and the local known_hosts database provide that second half of the identity check.

Separate first contact from rotation

With StrictHostKeyChecking=yes, SSH refuses unknown hosts and changed keys. That is the safest default for a fixed production endpoint, provided the expected key is installed through a trusted channel. accept-new is a narrower convenience for a fleet where new hosts are expected: it accepts a never-seen key but still refuses a changed key.

Host production-site
HostName www.example.test
User deploy
IdentityFile ~/.ssh/site_ed25519
StrictHostKeyChecking yes
UserKnownHostsFile ~/.ssh/known_hosts

Do not “fix” a warning by adding StrictHostKeyChecking=no to a deployment script. That converts a useful signal into silent acceptance. If a host is rebuilt, record the replacement fingerprint and review why the old key is no longer valid.

Make the fingerprint reviewable

Obtain the fingerprint from the host owner or console before the first connection, then compare it with what the client sees. A key change should have a ticket, maintenance note, or other explanation that another operator can inspect.

The same rule applies to automation: the known-hosts file is configuration with security consequences, not disposable cache data. Back it up with the deployment record, but do not publish private keys or copied credentials with the site artifact.

Sources

OpenBSD ssh_config, StrictHostKeyChecking and UserKnownHostsFile, checked 2026-07-28.
OpenSSH ssh-keygen manual, fingerprint inspection, checked 2026-07-28.

The advantage of small systems

Mon, 27 Jul 2026 00:00:00 +0000

Small does not mean unfinished. It means each component has a clear job, dependencies are deliberate, and the path from request to result remains visible.

Visibility is a feature

When operators can name every boundary, they can also identify which evidence is missing. Logs become more useful, alerts become more specific, and routine maintenance becomes less risky.

For a static website the important boundaries are usually easy to list:

DNS points the hostname to the intended edge.
TLS terminates at the intended proxy.
The proxy serves one known output directory.
The output contains only the files the site needs.
A 404 response is handled by the site, not by an accidental upstream.

Writing this list down is more valuable than adding a dashboard that does not answer any of those questions.

Complexity should earn its place

A new layer is worthwhile when it removes more uncertainty than it creates. A build step that fingerprints assets can be useful when caching is important. A database is useful when content needs transactions. Neither is automatically an improvement for a small, mostly static site.

The same rule applies to client-side JavaScript. If a page needs a search index or an interactive editor, add the smallest implementation that meets that requirement and update the content security policy deliberately. If the page is a document, plain HTML is often easier to inspect and more resilient.

Make ownership explicit

Every file should have a reason to exist and a clear way to update it. A vendored theme should record its upstream version and license. A generated directory should be marked as generated. A resource download should say what it contains, when it was updated, and how its checksum was produced.

These small statements prevent future operators from treating an accidental artifact as a supported interface.

Leave room for the next change

The best small system is not the one with the fewest lines. It is the one where the next change has a visible place to go. A notes site can start with Markdown, a static generator, and a web server; if it later needs search or comments, the new requirement can be evaluated on its own rather than assumed from the beginning.

Sources

Hugo directory structure, directory conventions for content and assets, checked 2026-07-27.
Caddy file_server directive, static file serving defaults referenced by the design, checked 2026-07-27.

Security headers should describe the actual page

Thu, 23 Jul 2026 00:00:00 +0000

Security headers are not a substitute for secure code, but they make the browser enforce useful boundaries. The policy should describe the page that is actually served, not a generic template copied from another project.

Start from the resource graph

If a site serves HTML, a local stylesheet, a favicon, and no executable JavaScript, a narrow policy can be understandable:

Content-Security-Policy: default-src 'self'; base-uri 'self'; form-action 'none'; frame-ancestors 'none'; object-src 'none'; script-src 'none'; style-src 'self'; img-src 'self' data:

The script-src ’none’ choice is only correct while the site does not require executable scripts. Adding search, comments, or an analytics tag changes the resource graph and should trigger a deliberate policy review.

Add transport and framing protections

For an HTTPS-only site, the following headers are common starting points:

Strict-Transport-Security: max-age=31536000; includeSubDomains
X-Content-Type-Options: nosniff
X-Frame-Options: DENY
Referrer-Policy: strict-origin-when-cross-origin
Permissions-Policy: camera=(), microphone=(), geolocation=(), payment=(), usb=()

Only enable HSTS with includeSubDomains when every subdomain is prepared to serve HTTPS. A header is a contract with future deployments, not merely a score in a scanner.

Check behavior, not just presence

Request a normal page, a missing page, and a static asset. Error responses should carry the same important security headers as successful responses. Also confirm that compression and caching do not change the content type or expose an internal path.

The Caddy example in this site is a starting point, not a universal policy. Adapt the host names, certificate handling, and application routes to your own deployment.

Sources

MDN: Content Security Policy guide, CSP directive names and syntax, checked 2026-07-23.
MDN: Strict-Transport-Security, HSTS directives and deployment cautions, checked 2026-07-23.
Caddy header directive, response header manipulation directives, checked 2026-07-23.

robots.txt and sitemaps answer different questions

Tue, 21 Jul 2026 00:00:00 +0000

Two small files are often treated as if they were a security boundary. They are not. A robots.txt file describes crawler preferences, while a sitemap gives search systems a list of URLs that belong to the site.

What robots.txt can and cannot do

The rules are published at the origin’s /robots.txt path and are read by cooperating crawlers. They do not protect a private directory, remove a URL from the network, or replace authentication. A route that must not be public needs server authorization or a network boundary.

Keep the file boring and test its actual location:

User-agent: *
Disallow:
Sitemap: https://www.example.test/sitemap.xml

The file should be UTF-8. If a deployment redirects it, verify the crawler behavior you intend rather than assuming every client follows the same chain.

What a sitemap adds

A sitemap is an inventory, not a permission list. Use absolute URLs from one host, encode XML values correctly, and include only canonical pages that you are prepared to publish. Do not list a URL merely because it exists in a build directory.

The protocol permits up to 50,000 URLs and 50 MB per sitemap file. A small site does not need an index file; one ordinary sitemap is easier to inspect. Validate it as XML and request it through the same HTTPS edge as a normal page.

curl -fsS https://www.example.test/robots.txt
curl -fsS https://www.example.test/sitemap.xml | xmllint --noout -

If xmllint is not installed, parse the XML in the same CI environment that publishes it. The important part is that the check runs before the file is replaced at the edge.

Sources

RFC 9309 — Robots Exclusion Protocol, robots rules, file location, and user-agent matching, checked 2026-07-21.
Sitemaps Protocol, sitemap XML structure and discovery, checked 2026-07-21.

Reliable defaults beat clever recovery

Mon, 20 Jul 2026 00:00:00 +0000

Small services often accumulate recovery logic before their normal path is fully understood. Every retry, alternate endpoint, and compatibility branch adds another state that must be observed and tested.

Make the common path boring

A useful default is explicit, easy to inspect, and safe to repeat. For a static site, that can be as simple as:

Build from a pinned toolchain.
Publish one complete directory.
Check the resulting HTML and assets.
Keep the previous directory available for rollback.

The sequence is less impressive than a multi-stage deployment system, but its state is visible. When something fails, the operator can answer whether the problem is in the source, the build, the copy, or the web server.

Retry only a bounded operation

Retries are useful when the operation is known to be transient and repeating it cannot create a second side effect. A download from an origin may be safe to retry; a database migration may not be. Treating every error as retryable hides the boundary that needs attention.

When a retry is appropriate, record the attempt count and the final reason. A log entry such as “publish failed: checksum mismatch” is more actionable than a sequence of silent retries followed by a generic timeout.

Prefer one authoritative state

Configuration, runtime state, and documentation should agree about which directory is live and which command produces it. If a release can be copied to three different paths depending on who runs it, recovery becomes guesswork.

For a static deployment, a short release record is enough:

release: 2026-07-20
source: git commit <commit-id>
builder: Hugo 0.165.0
output: public/
verification: links + headers + checksums

The placeholder commit ID is deliberately resolved at release time instead of being invented in documentation.

Recovery should restore a known state

Recovery is easiest when it returns the service to the last known-good directory, not when it chooses among several partially built alternatives. Keep the previous output until the new output has passed its checks, then remove old copies according to a retention policy.

The goal is not to eliminate failure. It is to make the failure small enough to explain and the recovery small enough to trust.

Sources

RFC 9110 — HTTP Semantics, section 9.2.2 on idempotent methods and retries, checked 2026-07-20.
Static-site release checklist, local companion resource.

A release manifest should name every published byte

Thu, 16 Jul 2026 00:00:00 +0000

A static artifact is a directory, not one executable. Recording only the source commit or only the homepage checksum leaves gaps: a missing image, stale alias, or changed download can survive unnoticed. A release manifest should enumerate every regular file.

Generate a stable list

Run the command from the artifact root so paths remain relative. Sort by path under a fixed locale:

cd public
find . -type f -exec sha256sum {} + | LC_ALL=C sort -k2 > ../release.sha256

The manifest is evidence about the artifact, so keep it outside the directory being measured unless the manifest itself is intentionally part of the release.

Verify after transport

On the destination, verify individual files:

cd /srv/www/site.new
sha256sum -c /path/to/release.sha256

This catches changed bytes and missing paths. It does not report unexpected extra files, so compare the destination file list too:

find . -type f | LC_ALL=C sort > destination.files
awk '{print $2}' /path/to/release.sha256 | LC_ALL=C sort > expected.files
diff -u expected.files destination.files

Add an aggregate digest for release records

Hash the manifest itself to produce a short identifier for logs and deployment records:

sha256sum release.sha256

The aggregate digest is only meaningful when the manifest generation rules are fixed: relative path form, sorting locale, hash algorithm, and whether generated metadata is included all belong in the procedure.

Do not confuse integrity with authenticity

SHA-256 proves that two byte sequences match. If an attacker can replace both the artifact and the manifest, the check does not establish who produced them. Artifact signing and trusted distribution are separate controls.

Sources

GNU Coreutils: sha2 utilities, checksum generation and checking, checked 2026-07-16.
sha256sum(1), command behavior and output format, checked 2026-07-16.

Redirects and error codes should preserve the story

Tue, 14 Jul 2026 00:00:00 +0000

An HTTP status is part of the interface. A browser may render a friendly page, but a monitor, crawler, cache, and API client also need the status code and headers to tell the same story.

Permanent moves are not all interchangeable

308 Permanent Redirect communicates that the resource has a new permanent URI while preserving the request method. That is important for a client that sends POST, PUT, or another non-GET method. A redirect from an old page to a new page is easy to test with GET; a migration of an endpoint must also be tested with the method that real callers use.

curl -sS -D - -o /dev/null --max-redirs 0 \
 https://old.example.test/api/item

Check that Location is absolute or correctly rooted, that the target is the intended host, and that the response is not silently downgraded to a temporary redirect. A 308 is cacheable by default, so change it only with a deliberate migration plan.

Distinguish missing from removed

Use 404 Not Found when the server cannot find a current representation and the absence may be temporary or unknown. 410 Gone is stronger: it says the resource was intentionally removed and is unlikely to return. Both should have a body that helps a human, but neither should return 200 just because a custom error page rendered successfully.

The check belongs at the edge:

curl -sS -o /tmp/missing.html -w '%{http_code} %{url_effective}\n' \
 https://www.example.test/a-route-that-does-not-exist

Keep the response headers on the error path. Security headers, a useful content type, and a correct status are more valuable than a decorative error animation.

Sources

RFC 9110 — HTTP Semantics, sections 15 and 13, checked 2026-07-14.
RFC 7538 — 308 Permanent Redirect, section 3, checked 2026-07-14.
curl manual, status and redirect inspection flags, checked 2026-07-14.

Read the public edge in two commands

Mon, 13 Jul 2026 00:00:00 +0000

A deployment is complete when the public edge agrees with the files you chose, not when the last upload command exits zero. Two read-only helpers from the operator kit make that agreement visible from any machine that can reach the host.

Inspect the response headers

check-http-headers.sh fetches one URL and prints the response line, the headers, and the final URL after redirects:

check-http-headers.sh https://www.xbcatm.com/

A recent read against this site produced:

HTTP/2 200
accept-ranges: bytes
content-security-policy: default-src 'self'; base-uri 'self'; form-action 'none'; frame-ancestors 'none'; object-src 'none'; script-src 'none'; style-src 'self'; img-src 'self' data:
content-type: text/html; charset=utf-8
last-modified: Mon, 24 Aug 2026 11:20:54 GMT
permissions-policy: accelerometer=(), camera=(), geolocation=(), gyroscope=(), microphone=(), payment=(), usb=()
referrer-policy: strict-origin-when-cross-origin
strict-transport-security: max-age=31536000; includeSubDomains
x-content-type-options: nosniff
x-frame-options: DENY

HTTP_STATUS 200
FINAL_URL https://www.xbcatm.com/

Two lines matter immediately: a 200 status with a FINAL_URL that matches the host you intended, and a Content-Security-Policy that still says script-src 'none'. If any of those differ from the policy you believe is live, the edge is not the tree you staged.

Inspect the certificate

check-tls-expiry.sh HOST [DAYS] reads the public certificate for the hostname and enforces a minimum validity window:

check-tls-expiry.sh www.xbcatm.com 30

A recent read printed:

subject=CN=www.xbcatm.com
issuer=C=US, O=Let's Encrypt, CN=YE1
notBefore=Aug 21 08:37:13 2026 GMT
notAfter=Nov 19 08:37:12 2026 GMT

certificate remains valid for at least 30 day(s)

Notice the subject is the exact hostname, not a wildcard from an adjacent site. notAfter is a concrete date; if it is closer than the window you passed, the helper exits non-zero and your release check can treat that as a failing condition.

Use both around a release

Once before and once after you swap directories:

Before: record last-modified, the CSP, and the certificate dates as your baseline.
Deploy the staged tree.
After: run the same two commands and compare last-modified and the checksums.

The two outputs together are a small but complete contract: the certificate is current, the policy is intact, and the bytes changing at the edge match what you published. That is the evidence a release claim is allowed to be.

Sources

Caddy Automatic HTTPS, automatic TLS certificate management, checked 2026-07-13.
MDN: Content Security Policy guide, CSP directive names and syntax, checked 2026-07-13.
OpenSSL s_client documentation, SNI and certificate inspection options, checked 2026-07-13.

A release is not complete until the public edge agrees

Thu, 09 Jul 2026 00:00:00 +0000

Static publishing removes application runtime complexity, but it does not remove the boundary between a generated directory and a public response. A release check should cover both.

Start from a clean artifact

Build with the pinned generator into a clean destination. Record the source commit, generator version, output file list, and checksums of files that users download. A clean build catches stale files that a copy-over deployment can accidentally preserve.

make verify
find public -type f -print | sort

The file list is evidence, not decoration. If a route disappears, the diff should explain whether the source was removed or the generator failed to emit it.

Exercise three response classes

Request one HTML page, one static resource, and one missing path. Inspect status, content type, cache policy, and security headers:

curl -fsS -D - -o /dev/null https://www.example.test/
curl -fsS -D - -o /dev/null https://www.example.test/downloads/check-http-headers.sh
curl -sS -D - -o /dev/null https://www.example.test/does-not-exist

The third command intentionally does not use -f: a 404 is the expected result and should still be captured. Compare the public body with the generated 404.html and verify that the status remains 404.

Keep rollback simple

Do not delete the previous directory until the new one has passed the checks. A rollback should select a known-good directory, not reconstruct one from memory during an incident. The release checklist and HTTP header check are deliberately small enough to run from a clean shell.

Sources

RFC 9110 — HTTP Semantics, status and representation semantics, checked 2026-07-09.
curl manual, response inspection options, checked 2026-07-09.
Static-site release checklist, local companion resource.

A postmortem should leave a fact record

Tue, 07 Jul 2026 00:00:00 +0000

A postmortem earns trust when its claims can be re-checked. That means every phase names the command that produced the fact, not a paraphrase of what someone remembers. The four phases below keep a write-up reviewable at any later time.

Detect: the symptom, with evidence

Start with the smallest verifiable symptom and the command that showed it. A capture is better than a prose description:

$ check-http-headers.sh https://www.xbcatm.com/
HTTP/2 200
content-security-policy: ... script-src 'none' ...
last-modified: Mon, 24 Aug 2026 11:20:54 GMT

If the symptom is that a header changed, the output showing the previous policy and the new one belongs side by side. If it is a failure, include the exit status and the error line.

Scope: how wide, and how you know

State the blast radius with evidence, not adjectives. Fix the boundary you can inspect:

Which hosts or paths reply with the same symptom? One check-http-headers.sh per candidate host answers this.
Does the cache differ from origin? Compare Vary and validators.
Which rollback window applies? Use the TTL that was in force before the change.

Fix: the change and its intended effect

Write the corrective action so it can be replayed. Prefer the smallest change that restores the contract, and name what the post-fix run should show:

# new policy line expected in the response:
script-src 'none'

Verify: the post-incident run

Repeat the detection command after the change and show that the observed output now matches the intended contract. A postmortem without this final section is a story; with it, it is a record that approves its own future re-check.

Sources

RFC 9110 — HTTP Semantics, response metadata and conditional requests, checked 2026-07-07.
artifact HTTP header check, read-only inspection used throughout this record.

Range requests should prove which bytes were selected

Mon, 06 Jul 2026 00:00:00 +0000

Range requests let a client ask for part of a representation. Media players, resumable download tools, and diagnostic clients use them, but a server that advertises or returns ranges incorrectly can produce silent corruption instead of a clean failure.

Establish the complete size

Fetch headers for the complete representation and record its length and validator:

url=https://www.example.test/downloads/archive.tar.gz
curl -sS -D full.headers -o /dev/null "$url"
awk 'tolower($1) ~ /^(content-length:|etag:|last-modified:|accept-ranges:)$/ { print }' full.headers

Accept-Ranges: bytes is an explicit signal, but absence of the header does not by itself prove that range requests are unsupported. Exercise the request.

Request a known interval

Ask for the first 16 bytes and keep both headers and body:

curl -sS -D range.headers -o range.body \
 -H 'Range: bytes=0-15' "$url"

wc -c range.body
awk 'tolower($1) ~ /^(content-range:|content-length:|etag:)$/ || /^HTTP\// { print }' range.headers

A successful byte-range response uses 206 Partial Content. Content-Range should identify 0-15 and the complete representation length, while the body should contain exactly 16 bytes.

Test an impossible range

Request bytes beyond the known end:

curl -sS -D - -o /dev/null \
 -H 'Range: bytes=999999999-' "$url"

For an unsatisfiable byte range, 416 Range Not Satisfiable and a Content-Range value such as bytes */12345 make the actual length visible. A 200 response may be valid when the server ignores the range, but it must return the complete representation rather than a mislabeled fragment.

Keep validators in the story

Resumed downloads can use If-Range with a strong validator or date. If the representation changed, the safe response is the full current representation, not bytes spliced from two versions. Test this behavior before calling a download resumable.

Sources

RFC 9110 — HTTP Semantics, range units, partial responses, and Content-Range, checked 2026-07-06.
curl manual, --range and header options, checked 2026-07-06.

HTTP methods are a promise about side effects

Thu, 02 Jul 2026 00:00:00 +0000

A request method is a promise about side effects, not just a verb you pass to a client. When the origin is a static file tree, most of that promise is already settled before the first request: the tree has no transactions, so methods that would mutate state have nothing safe to mutate.

The method is part of the contract

HTTP method semantics are defined in RFC 9110. GET and HEAD must be safe: they promise a client that the request does not change server state. PUT, POST, and DELETE are not safe by default; they may change state. A server that cannot honor the promise should say so with an explicit status, not with a guessed body.

For a static site the useful distinctions are:

GET returns the representation.
HEAD returns the same response metadata without the body.
OPTIONS discloses what the origin will accept.
POST / PUT / DELETE / PATCH have no meaning for an immutable file tree and should be rejected.

What a Caddy static origin actually answers

Point curl at the public edge and the method boundary is easy to read. An OPTIONS request against a site that only serves files returns 405 Method Not Allowed:

$ curl -s -o /dev/null -w 'OPTIONS -> HTTP %{http_code}\n' -X OPTIONS https://www.xbcatm.com/
OPTIONS -> HTTP 405

A 405 with an Allow header naming the supported methods is the correct, explicit reject. Compare this with a dynamic origin that happens to ignore the body: an imported handler can turn a universal non-promise into silent success, which hides the actual contract.

HEAD should equal GET except for the body

Because HEAD is safe and body-free, its metadata should match the equivalent GET. Content-Length still describes the bytes a GET would return. On this site both agree:

HEAD content-length: 15890
GET bytes read : 15890

If a proxy strips or rewrites Content-Length on HEAD, a checker that compares the two will catch it. This is the parity the head-request-parity note and the check-http-headers.sh helper both rely on.

What to do when a client sends a mutating method

Answer explicitly. Return 405 Method Not Allowed with an Allow header listing the safe methods, rather than falling through to a page that looks successful. The HTTP foundations path depends on a single obvious answer at the edge: every method is either supported with its documented semantics or rejected with a status that says so.

Sources

RFC 9110 — HTTP Semantics, method definitions, safe/idempotent methods, and 405, checked 2026-07-02.
MDN: HTTP request methods, method semantics and 405 behavior, checked 2026-07-02.
curl manual, -X, -o, and -w inspection options, checked 2026-07-02.

Validators decide whether a cached copy is still the answer

Tue, 30 Jun 2026 00:00:00 +0000

A cache does not re-download a document every time it wants to know whether its copy is current. Instead it sends a validator back to the origin and lets the origin answer with a small 304 Not Modified, or with the new body. Validation is the second half of HTTP caching, and validators are the keys that make it cheap.

A validator is a currentness answer you can compare

A validator is metadata that changes when the representation changes. HTTP defines two families:

Strong validators (ETag) identify a specific version of the bytes. Comparing them is reliable.
Weak validators (Last-Modified) are timestamps with second granularity; they can miss two writes in the same second.

An origin should send at least one validator. Caddy serves files with both ETag and Last-Modified by default, so the public edge of this site returns both:

etag: "dkx84jwth7nkc9e"
last-modified: Mon, 24 Aug 2026 13:55:23 GMT

Conditional requests trade a header for a possible 304

A client asks with If-None-Match (or a validator it already holds) and the origin compares it to the current one. When they match, the origin confirms it without resending the body:

$ curl -s -o /dev/null -w 'HTTP %{http_code}\n' -H 'If-None-Match: dkx84jwth7nkc9e' https://www.xbcatm.com/
HTTP 304
$ # size_download == 0 on a revalidation hit

When they differ, or no validator was sent, the origin answers 200 with the fresh body. A 304 is not a failure: it is the cheaper way to say the cached copy is still valid.

Strong and weak are not interchangeable

Use the strong ETag for conditional GET so the comparison is authoritative. Weak validators only promise that a body has stayed semantically similar, which is why range requests prefer strong ones. The http-range-requests note covers byte selection; this note covers “is my stored copy still the answer”.

What changes when you republish

When the tree changes, the ETag for a page changes too, so caches that revalidate fetch the new body. If a release updates bytes without touching Last-Modified, the ETag still catches the change, which is why the release manifest records byte checksums rather than only file mtimes.

Sources

RFC 9110 — HTTP Semantics, validators, ETag, and conditional request fields, checked 2026-06-30.
RFC 9111 — HTTP Caching, freshness, If-None-Match, and 304, checked 2026-06-30.
MDN: HTTP conditional requests, 304 and validator behavior, checked 2026-06-30.

Compression changes the selected HTTP representation

Mon, 29 Jun 2026 00:00:00 +0000

Compression saves transfer bytes, but it also creates another representation of a resource. A client announces acceptable content codings with Accept-Encoding; the server describes the applied coding with Content-Encoding.

Make negotiation visible

When a response can change according to Accept-Encoding, include that request field in Vary. This tells shared caches that a compressed response and an identity response are not interchangeable cache entries.

Compare the two paths instead of checking only a browser request:

curl -sS -D - -o /dev/null \
 -H 'Accept-Encoding: identity' https://www.example.test/
curl -sS --compressed -D - -o /dev/null \
 https://www.example.test/

Inspect Content-Encoding, Vary, Content-Length when present, and the validator. A server can use different entity tags for differently encoded representations; what matters is that conditional requests validate the same selected representation consistently.

Compress appropriate content

Text formats such as HTML, CSS, JSON, XML, and SVG usually benefit from compression. Formats that are already compressed might not. Caddy’s encode directive negotiates supported encodings and normally avoids encoding a response without an appropriate content type or minimum size.

Do not add compression solely to satisfy a score. Measure a representative response, confirm that the edge emits the intended headers, and verify that downloadable files retain the correct content type and checksum after transfer decoding.

Sources

RFC 9110 — HTTP Semantics, content codings and Vary, checked 2026-06-29.
Caddy encode directive, content encoding selection and negotiation, checked 2026-06-29.
curl manual, --compressed, checked 2026-06-29.

Cache headers are a contract with two clocks

Thu, 25 Jun 2026 00:00:00 +0000

Caching is not a single switch. A response has a freshness decision made by a cache and a validation conversation with the origin. Mixing those two ideas produces either stale content or needless requests.

Pick the change model first

For an HTML document that may change after publication, Cache-Control: no-cache is usually a more accurate starting point than no-store. no-cache permits storage but requires a cache to validate before reuse; no-store asks caches not to store the response at all. The distinction matters when you want conditional requests and a cheap 304 Not Modified response.

For a fingerprinted asset such as app.4f2c.js, the URL changes when the bytes change. A long freshness lifetime can then be reasonable:

Cache-Control: public, max-age=31536000, immutable

That policy is unsafe for a stable URL whose contents can be replaced in place. If the URL is stable, prefer a shorter lifetime and a validator such as an entity tag (ETag) or a meaningful Last-Modified value.

Inspect both paths

Make one ordinary request and one conditional request. The exact server flags vary, but the evidence you want is stable:

curl -sS -D - -o /dev/null https://www.example.test/
curl -sS -D - -o /dev/null \
 -H 'If-None-Match: "copy-a-real-etag-from-the-first-response"' \
 https://www.example.test/

Do not paste a made-up validator into a runbook. Copy the value from the first response or use a test fixture. A successful revalidation should return 304 only when the server can prove that the selected representation has not changed.

Keep intermediaries visible

Age, Vary, and the cache-control directives explain why two clients can receive different results. If a response varies by Accept-Encoding, language, or another request field, that dimension belongs in Vary; otherwise a shared cache can reuse the wrong representation.

The useful release check is not “the scanner found a cache header”. It is “the header matches the replacement policy, and a conditional request behaves as documented”.

Sources

RFC 9111 — HTTP Caching, sections 4–5, checked 2026-06-25.
RFC 9110 — HTTP Semantics, sections 8 and 13, checked 2026-06-25.
MDN: Cache-Control, directive semantics and defaults, checked 2026-06-25.

HSTS should be rolled out with a recovery plan

Tue, 23 Jun 2026 00:00:00 +0000

HTTP Strict Transport Security tells a supporting browser to use HTTPS for a host during a cached period. That persistence is the feature and the risk: removing the header does not immediately erase policy already stored by clients.

Verify the HTTPS path first

Before sending HSTS, confirm that the canonical hostname serves a valid certificate and that HTTP redirects to the intended HTTPS URL without depending on user input:

curl -sS -D - -o /dev/null --max-redirs 0 http://www.example.test/
curl -sS -D - -o /dev/null https://www.example.test/

Check representative deep routes and error pages. HSTS cannot repair a certificate error because the browser requires a valid HTTPS connection before accepting the policy.

Start with a short max-age

A staged rollout limits the recovery window while configuration is new:

Strict-Transport-Security: max-age=300

After observing the site and renewal path, increase the duration deliberately. Record the date, chosen value, and rollback conditions. A final policy might use a year, but the number is a commitment rather than a scanner score.

Treat includeSubDomains as a separate decision

includeSubDomains extends policy to every subdomain. Inventory names first, including old services, delegated zones, and hostnames used only on internal networks. One HTTP-only descendant is enough to make the option disruptive for clients that received the parent policy.

Preload is not ordinary header configuration

Browser preload programs can distribute policy outside the normal response cycle. Their requirements and removal delays are stricter than setting a header. Do not request preload merely because a scanner recommends it; confirm long-term ownership of the domain and all covered names.

Verify the public response

curl -sS -D - -o /dev/null https://www.example.test/ \
 | awk 'tolower($1) == "strict-transport-security:" { print }'

Test the canonical public edge, not only an origin port. Proxies may add, remove, or duplicate the header.

Sources

RFC 6797 — HTTP Strict Transport Security, policy processing and scope, checked 2026-06-23.
MDN: Strict-Transport-Security, directives and deployment cautions, checked 2026-06-23.

HEAD should describe the same representation as GET

Mon, 22 Jun 2026 00:00:00 +0000

The HEAD method asks for the response a server would send to GET, without transferring the response content. It is useful for checks that need status, validators, type, or length, but only when the metadata remains aligned with the real GET path.

Compare a normalized header set

Dynamic headers such as Date will differ between requests. Compare the fields that describe the selected representation:

url=https://www.example.test/downloads/manual.pdf

curl -sS -I "$url" > head.headers
curl -sS -D get.headers -o /dev/null "$url"

for file in head.headers get.headers; do
 printf '== %s\n' "$file"
 awk '
 /^HTTP\// ||
 tolower($1) ~ /^(content-type:|content-length:|content-encoding:|cache-control:|etag:|last-modified:|vary:)$/ { print }
 ' "$file"
done

The two requests should select the same status and representation metadata. Compression negotiation also belongs in the comparison: send the same Accept-Encoding value to both requests.

Do not use HEAD as the only release check

A server can synthesize plausible headers while the file is missing, unreadable, or truncated. Keep one small GET in the smoke test and verify its body or checksum. HEAD reduces transfer cost; it does not prove the payload.

Check redirects explicitly

Without --location, curl -I reports the first response. That is useful when testing redirect policy. With --location, it reports the final chain, which is useful when testing the destination. Record which question the command answers:

curl -sS -I --max-redirs 0 https://old.example.test/manual
curl -sS -I --location https://old.example.test/manual

Treat method-specific failures as configuration defects

A static page that returns 200 to GET and 405 or 404 to HEAD usually exposes a proxy or routing inconsistency. Fix the method handling instead of teaching monitors to ignore it, unless the endpoint contract deliberately disallows HEAD.

Sources

RFC 9110 — HTTP Semantics, HEAD method semantics, checked 2026-06-22.
curl manual, --head, --include, and redirect options, checked 2026-06-22.