smart-restart

Rules-as-config restart decider for Python services. Don't restart your whole stack on every git push.

The problem

You ship a one-line bug fix to one service in your monorepo. Your deploy script restarts everything — bot, API, worker, scheduler — and you eat 30 seconds of cold starts and dropped connections, every time.

Most CI/CD scripts pick between two extremes:

• Restart everything always. Safe, but wasteful and slow.
• Hand-maintained "if file in dir then restart X." Fast, but rots silently when imports cross boundaries: someone refactors utils/db.py and forgets that worker/jobs.py imports it, the worker keeps the old code, you get a Heisenbug at 3 a.m.

smart-restart is the middle ground: a small decider that takes the list of changed files and a YAML rule set, then prints which actions are needed. Optionally, it walks the AST-derived import graph in reverse so editing a leaf utility correctly triggers restarts for every service that imports it.

It does not run the actions. Your deploy script does. smart-restart just decides.

Quick start

pip install smart-restart  # coming with v0.1.0

Write a restart-rules.yaml:

actions:
  pip_install:
    order: 10        # lower = runs earlier
  restart_api:
    order: 20

rules:
  - pattern: "requirements.txt"
    actions: [pip_install, restart_api]
  - pattern: "src/**"
    actions: [restart_api]
  - pattern: "**/*.md"
    actions: []      # explicitly do nothing

fallback: [restart_api]   # for files that match no rule

Pipe a diff into it:

$ git diff --name-only HEAD~1 HEAD | smart-restart
pip_install
restart_api

That's the output your deploy script consumes. Wire it into bash, Ansible, GitHub Actions, anything that takes stdout.

Import-chain expansion (the interesting bit)

The base decider only knows about files you literally changed. That misses the case where a leaf module changes and dependents don't.

Pass --root <project> and smart-restart will parse every .py file under <project>, build a static import graph, and expand the changed file list to include every transitive importer:

src/
  utils/db.py        # you changed this
  api/handlers.py    # imports utils.db
  worker/jobs.py     # imports utils.db

$ echo "src/utils/db.py" | smart-restart --root src --show-expanded
INFO: import-chain expansion added 2 file(s):
  + smart_restart/api/handlers.py
  + smart_restart/worker/jobs.py
restart_api
restart_worker

If restart-rules.yaml only matches src/api/** to restart_api and src/worker/** to restart_worker, the expansion ensures both fire even though only db.py was in the diff.

--root and src-layout

If your project uses src-layout (code under src/your_pkg/), pass --root src, not --root .. The graph indexes files by their dotted module name; the dotted name has to match what your imports actually say (from your_pkg.foo resolves to <root>/your_pkg/foo.py).

Why a separate decider

• One source of truth. Change restart-rules.yaml, every script that consumes the decider stays in sync.
• Composable. Pipe it into bash, Ansible, GitHub Actions, anything that takes stdout. No framework lock-in.
• Diffable. Restart rules live in version control, not buried in a shell script.
• Testable. Pure function, no side effects, hermetic.

Configuration reference

actions:                 # required: action name -> {order: int}
  <name>:
    order: <int>         # lower = runs earlier; default 100

rules:                   # required: list, evaluated top-down, first match wins
  - pattern: <glob>      # ** matches across directories, * within one segment
    actions: [<name>...] # actions to fire (use [] to explicitly skip)

fallback:                # what to do for files that match no rule
  none                   # default: contribute no actions
  | all                  # fire every declared action
  | [<name>...]          # fire just these

First-match-wins semantics: each file is matched against rules top-to-bottom, only the first hit contributes. This lets you put a narrow **/*.md → [] rule above a broad src/** → [restart_api] rule.

Status

🚧 Alpha — extracted from a closed-source dogfood project (~2 years of daily use).

Done in v0.1:

• Generic rule engine with first-match-wins semantics
• YAML-declared actions (no hardcoded service names)
• Import-chain reverse closure (AST-based)
• Glob patterns with ** recursion
• Pure decider — no execution, no side effects
• 37 unit tests, fixture-driven

Deferred to v0.2+:

• LLM fallback for unmatched files (the upstream project has it; needs to be re-cast as a plugin to keep v0.1 dependency-free)
• Multi-root graph merge in one invocation
• Auto-detection of src-layout from pyproject.toml
• Star-import edge tracking at the symbol level

License

MIT