Operations

A postmortem should leave a fact record

A postmortem is a chronological map from detected symptom to verified fix, backed by the commands that produced each fact.

A service boundary blocks an unwanted write while a deliberate opening leads to writable state.

Harden a systemd service by testing its boundaries

Service hardening should turn a specific unwanted operation into a denied operation while preserving the work the application must perform. systemd supplies execution settings for filesystem views, namespaces, privileges, and other resources. They are separate controls with separate limits. Adding four familiar directives does not make every readable file, reachable process, inherited descriptor, or allowed system call disappear. ...

A green validity interval includes filled notBefore and notAfter endpoints; times outside are crossed out. A second example fails at hour four because the issuer expired at hour three while the leaf lasts six hours.

A TLS certificate expiry is a date you can read

A certificate’s expiry is a deadline for certificate validation, not a timer that necessarily closes every existing connection. Read the certificate actually served to the intended hostname, then distinguish its validity window from the rest of the trust decision. A future notAfter date alone does not establish that HTTPS is healthy. ...

The old endpoint keeps serving across the DNS switch while the new endpoint is already ready. The overlap continues into observation; changing TTL cannot rewrite cached answers.

DNS changes need a cache-aware rollback window

Prepare the TTL ahead of time, observe authoritative and recursive answers, and keep both endpoints valid through the cache window.

The authority lowers address A from TTL 8 seconds to 3 seconds while one resolver’s previously stored A answer continues its original received lifetime.

Lower DNS TTL before a move and budget the rollback cache window

Lower the TTL early if you expect to move a hostname.

An editable version 2 source waits for a rebuild while the public directory still serves version 1 to requests. The pause marks the unpublished edit; saving does not publish it.

Why a small site can stay static

A static origin is a boundary you can name, cache, and roll back.

Retrieve an archive and checksum from storage, verify the retrieved copy before use, and restore into an isolated disposable test target. Check files, permissions and elapsed restore time. A stored file alone is not proof of recovery.

Backups are only useful after a restore rehearsal

Choose a small recovery unit, verify it, and practice restoring it somewhere disposable.