Idempotence

An agent run that continues without a person watching, started by a schedule, an event, or a handoff, and reports its results when done.

A data structure whose replicas can be edited independently and always converge without coordination.

Sharing a copy until the moment one side writes to it, deferring the cost of duplication until it's actually needed.

Time-based scheduling of recurring jobs, and the reasons scheduled jobs quietly stop working.

Keeping several open tabs of the same app consistent, best done by broadcasting small notifications and letting each tab re-read the truth.

A versioned, ordered change to a database schema, applied once and recorded.

A SIM soldered into the device and provisioned over the air, with profiles downloaded rather than cards swapped.

The job of pulling data out of operational systems, cleaning and reshaping it, and loading it somewhere it can be analyzed, and the move from transforming before loading to transforming after.

A guarantee that replicas converge given no further updates, without guaranteeing when.

The small number every process returns when it ends, zero for success and anything else for failure, and the conventions that let shells, CI systems, and init systems act on it.

Waiting longer after each failed attempt, with a dose of randomness, so retries give a struggling system room to recover instead of hammering it.

A point-in-time, near-free copy of a filesystem's state, made possible by sharing unchanged blocks with the live data.

A key-value structure that uses a digest of the key to index an array of buckets.

The three-digit number at the start of every HTTP response that tells the client, caches, crawlers and monitoring what happened, grouped into five classes by the first digit.

A unique token a client attaches to a request so the server can recognize a retry and return the original result instead of doing the work twice, the standard defense against double charges and duplicate orders.

A buffer that decouples a producer from a consumer in time, so neither has to be up, fast, or reachable at the same moment.

A wrapper type with a way to lift a value in and a way to chain functions that return more wrappers.

Letting concurrent writers proceed unchecked and catching conflicts only at commit time, betting that collisions are rare.

An architecture where participants communicate directly rather than through a central server.

A defect whose occurrence depends on the relative timing of concurrent operations.

Data organized as tables with declared relationships, queried declaratively and guarded by constraints.

Initial content created programmatically to make an empty system usable or demonstrable.

The small coordination service peers use to find each other before connecting directly.

A design lineage in which high difficulty is a deliberate authorial position, sustained by making every death legible.

A file that points at another path, resolved transparently by most operations.

Civil time is a political layer over solar time, and its rules change often enough to be data.

The limit on how long to wait for a remote call, the most basic defense against a hung dependency, and the harder problems of choosing the number and passing the remaining time down a chain of services.

A 128-bit identifier that any machine can generate without coordination and still be practically certain no one else will produce the same one.

Inserting a row if it doesn't exist and updating it if it does, in one atomic statement, which is harder than it sounds because the obvious check-then-insert version races with itself.

A webhook is an HTTP callback a service pushes to you when an event happens, inverting who initiates the request.

The browser standard for direct peer connections carrying audio, video, and arbitrary data.

Recording the intent of a change durably before applying it, so a crash can be recovered.