DNS Changes Need TTL Math
A record saved at the provider is not live until TTLs expire and an independent resolver agrees.
Independent infrastructure notes
Jerry Labs
Field notes for keeping small internet services observable, recoverable, and boring to operate.
Written for the moment when a dashboard says healthy but the socket, certificate, firewall, or backup disagrees.
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Selected notes
Start with the live system, keep the evidence, and make the rollback path explicit before changing state.
One Port Number, Two Owners
Map TCP and UDP separately so listener ownership, firewall rules, and external tests describe the same service.
A Local SSH Tunnel Is a New Socket
Reach a loopback-only service without exposing its port, then prove the policy with a fresh SSH connection.
BBR vs Cubic: Test the Socket You Care About
Compare the controller on the active TCP socket while keeping latency, CPU, retransmissions, and timeouts visible.
Copying a Live SQLite File Is Not a Backup
Create an online snapshot with SQLite's backup API, verify it independently, and rehearse restore away from production.
Reading paths
Each note is self-contained. These paths group the checks that are commonly used in the same maintenance window.