Glossary

Terms used across these pages, in the order the pipeline meets them.

Atlas-lang — the bounded interpreter that executes a config. Python syntax, without any construct that would let the result depend on anything other than the config text and its declared inputs: no clock, randomness, environment, network or filesystem. See what config may not do.

Fuel — the step budget for an evaluation. A runaway computation stops with a FuelExhaustedError instead of hanging.

Input — a per-run value the config may branch on, supplied by -var, --var-file or [inputs]. The determinism guarantee is over (config, inputs, selected environments), not config alone. Not for secrets.

Config — the checked-in environment matrix: every environment and what differs between them, declared once as Config(AppEnv, envs={...}) and validated on construction. An input, by contrast, is a per-run value from outside the repository. See Environments.

EnvSchema — the shape of one environment, declared as a class of annotated fields. It is the only class Atlas-lang admits, because it is a declaration, not a computation. It makes env.domain complete in an editor and env.domian a type error. The untyped alternative is a mapping of var() declarations.

Environment — one entry in a Config. Its name is its stack's name, and --env narrows a run to it. An environment left out is out of scope, not undeclared: its state is not diffed and is never planned for deletion.

Resource — one managed thing, declared with a logical name. Its fields carry their own mutability.

Logical name — the name you give a resource in config. Node id — what it becomes once scoped: {stack}:{type}:{name}, e.g. prod:aws.S3Bucket:assets. Most commands accept a short form or a glob in place of a full id.

Stack — a namespace scoping region, tags and name prefix over the resources declared in its body.

Component — several resources behind one parameterized object. Written in Python, used by config, never defined by it. The children become ordinary flat resources named {component}-{child}.

Ref — the lazy handle returned by reading a computed field. The read creates the dependency edge; the Ref resolves to a real value at apply.

Mutability — each field is mutable() (in-place UPDATE), immutable() (REPLACE) or computed() (never diffs; produced by the provider).

IR — the intermediate representation: the content-hashed, provider-stamped graph a config lowers to. Everything downstream works on the IR, not on the source.

Canonical form — RFC 8785 JSON. Fixes key order, number formatting and string escaping, so the same IR always serializes to the same bytes and the content hash is stable.

input_hash — a node's Merkle hash: its own canonical inputs folded together with its dependencies' hashes. Unchanged hash, no provider call. See The Merkle hash.

Symbolic ref — the hash is computed over the reference to an upstream value, not over the resolved value (which does not exist yet at plan time).

Diff — the comparison of desired input_hashes against those recorded in state. It compares against recorded inputs, not the live world; comparing against the live world is refresh.

Changeset — the result: one action per node — NOOP, CREATE, UPDATE, REPLACE or DELETE.

Conditional replace — a REPLACE caused by an immutable field holding a Ref. It becomes a no-op if the value resolves unchanged at apply.

Plan — the ordered, guarded, policy-checked changeset.

Policy — a check over one node's pending change, evaluated at plan time. MANDATORY blocks, ADVISORY warns. See Policies.

Lease / lock — the time-bounded claim a run takes on state before writing. Renewed while the run lives; lapses if it dies.

Fenced write — a state write that succeeds only if the writer is still the recorded lease holder. The store makes the check, not the writer, which prevents two concurrent runs from silently merging state.

Compensation — the undo recorded for a completed node, run in reverse completion order when an apply fails. See When apply fails.

Poisoned row — a state row whose input_hash is cleared so the next plan cannot Merkle-skip it. Set before a compensation runs, so a rollback that fails mid-way cannot leave a silent divergence.

Plan drift — the changeset about to execute differs from the one that was approved, because state moved between the two. Raised, not reconciled.

Drift — the live world differing from what state records. Found by refresh, and only in the fields a provider's read reports.

Artifact (.atlas) — a compiled, content-hashed config with provider versions pinned. deploy applies it without re-executing the config, so identical bytes are promoted between environments.

Output — a value exported with output(), namespaced by its stack and persisted into state after apply. Read back with atlantide output, or from another stack via StackReference.

Secret — a name, not a value. atlantide.secret("x") returns a SecretRef; the plaintext is resolved in-memory at apply and never reaches the IR, the artifact or state.