Gpc Train

GPC Release Train

When to use

Use this skill when the task involves:

• Setting up a config-driven staged rollout pipeline
• Automatically progressing a release through tracks (internal → alpha → production) with time gates
• Gating progression on crash rate and ANR rate thresholds
• Pausing, resuming, or aborting an in-flight release train
• Checking the current stage and gate health of a running train

Inputs required

• Package name (or configured default in .gpcrc.json)
• Release train config: stages with tracks, rollout percentages, and time delays
• Gate thresholds: max crash rate and max ANR rate
• Whether to pause, resume, or abort the train

Procedure

1) Configure the release train

Add a release-train block to .gpcrc.json in the project root:

{
  "release-train": {
    "stages": [
      { "track": "internal",   "rollout": 100 },
      { "track": "alpha",      "rollout": 100, "after": "2d" },
      { "track": "production", "rollout": 10,  "after": "7d" },
      { "track": "production", "rollout": 100, "after": "14d" }
    ],
    "gates": { "crashes": { "max": 1.5 }, "anr": { "max": 0.5 } }
  }
}

Config keys:

Read:

• references/rollout-pipeline.md

2) Start the train

gpc train start

This reads .gpcrc.json, creates a state file at ~/.cache/gpc/train-<packageName>.json, and begins executing the first stage immediately. Subsequent stages are executed when the after time has elapsed and gates pass.

# Resume a paused train
gpc train start --resume

3) Check train status

gpc train status

Output:

Release Train · com.example.app
  Stage 2 / 4   alpha @ 100%   in progress
  Last progressed: 2026-03-17 11:00 (2 days ago)
  Next stage: production @ 10%   eligible in 5 days

  Gates (last check: 10 minutes ago)
    crashes   0.82%   ✓  (max 1.5%)
    anr       0.19%   ✓  (max 0.5%)

# Resume if paused due to a gate failure
gpc train status --resume

4) Monitor gate health

Before each stage transition, gpc train automatically checks the configured gates:

• If all gates pass, the stage progresses (subject to the after time having elapsed).
• If any gate fails, progression is paused and a warning is shown.
• The user must fix the regression and re-run gpc train start --resume or gpc train status --resume.

Gate checks call the same vitals API as gpc vitals crashes and gpc vitals anr. Data lag of 6–48 hours applies to new releases — avoid configuring gates on the very first stage.

5) Pause a running train

gpc train pause

Pauses automatic progression. Does not halt or change the active rollout on any track. Run gpc train start --resume to continue.

6) Abort the train

gpc train abort

Aborts the train and halts all active rollouts on tracks managed by this train. State file is cleared. Use when a critical regression is found and the release must be stopped immediately.

Verification

• gpc train status shows the correct current stage and gate health values
• gpc status confirms rollout percentages on each track match the active stage in the train config
• Gate values (crashes, ANR) are below configured max thresholds
• State file at ~/.cache/gpc/train-<packageName>.json reflects the current stage index and last progression timestamp

Failure modes / debugging

Read:

• references/rollout-pipeline.md — full lifecycle: config → start → gate check → progress → complete

Related skills

• gpc-release-flow: Upload, promote, and manual rollout management
• gpc-vitals-monitoring: Crash and ANR monitoring used by gate checks
• gpc-ci-integration: Running gpc train in CI/CD pipelines