Result JSON

Overview

When RESULT_FILE is set, migetpacks writes a JSON file containing build metadata after every build. This file is used by post-build steps (e.g., deployment pipelines, notification services) to determine build status and access image information.

The builder always exits with code 0 to ensure post-build steps (like Shipwright callbacks or sidecar containers) always execute. Check the status field in the result JSON to determine if the build actually succeeded or failed.

Schema

Field	Type	Description
`status`	`"success"` or `"failed"`	Build outcome
`exit_code`	number	Docker build exit code (0 on success)
`error`	string	Error message (only present on failure)
`images`	array	Built images with detected ports
`processes`	object	Process types from Procfile
`env`	object	Environment variables from app.json
`formation`	array	Process formation from app.json
`scripts`	array	Deployment scripts from app.json
`addons`	array	Service dependencies from app.json
`build_time`	number	Build duration in seconds
`language`	string	Detected or specified language
`timestamp`	string	ISO 8601 build completion time
`_shell`	boolean	`false` for distroless/DHI containers (no shell available)

images

{
  "images": [
    {
      "name": "registry.io/your-org/your-app:latest",
      "ports": ["5000/tcp"]
    }
  ]
}

For Docker Compose builds, multiple images are listed:

{
  "images": [
    {"name": "registry.io/myapp-api:latest", "ports": ["5000/tcp"]},
    {"name": "registry.io/myapp-web:latest", "ports": ["3000/tcp"]}
  ]
}

processes

Parsed from the application’s Procfile:

{
  "processes": {
    "web": "bundle exec puma -C config/puma.rb",
    "release": "bundle exec rails db:migrate",
    "workers": [
      {"name": "sidekiq", "command": "bundle exec sidekiq"},
      {"name": "clock", "command": "bundle exec clockwork clock.rb"}
    ]
  }
}

web — the primary web process (from RUN_COMMAND, Procfile web:, or language default)
release — one-time release command (e.g., database migrations)
workers — background worker processes (all non-web, non-release Procfile entries)

env

Environment variables defined in app.json:

{
  "env": {
    "SECRET_KEY_BASE": "a1b2c3d4e5f6...",
    "RAILS_ENV": "production",
    "DATABASE_URL": null
  }
}

Variables with "generator": "secret" have auto-generated values
Variables with "value": "..." use the specified value
Variables with "required": true are null (must be provided at deploy time)

formation

Process configuration from app.json:

{
  "formation": [
    {"name": "web", "quantity": 2, "size": "standard-1x"},
    {"name": "worker", "quantity": 1, "size": null}
  ]
}

scripts

Deployment scripts from app.json:

{
  "scripts": [
    {"name": "postdeploy", "command": "bundle exec rails db:migrate"},
    {"name": "pr-predestroy", "command": "bundle exec rails db:drop"}
  ]
}

addons

Service dependencies from app.json:

{
  "addons": [
    {"plan": "heroku-postgresql:hobby-dev", "as": null, "options": null},
    {"plan": "heroku-redis:premium-0", "as": "CACHE", "options": null},
    {"plan": "mongolab:shared-single-small", "as": "MONGO", "options": {"version": "5.0"}}
  ]
}

plan — the addon plan identifier
as — attachment alias (overrides config var prefix), or null
options — provider-specific options object, or null

_shell

Indicates whether the runtime container has a shell available:

{
  "_shell": false
}

When _shell is false (DHI/distroless images), deployment systems should:

Use exec format for commands (no /bin/sh -c wrapper)
Pre-expand shell variables like ${PORT:-5000}
Avoid relying on shebangs in scripts

Success Example

A complete result file for a successful Ruby build:

{
  "status": "success",
  "exit_code": 0,
  "images": [
    {
      "name": "registry.io/your-org/your-app:latest",
      "ports": ["5000/tcp"]
    }
  ],
  "processes": {
    "web": "bundle exec puma -C config/puma.rb",
    "release": "bundle exec rails db:migrate",
    "workers": [
      {"name": "sidekiq", "command": "bundle exec sidekiq"}
    ]
  },
  "env": {
    "SECRET_KEY_BASE": "a1b2c3d4e5f6789...",
    "RAILS_ENV": "production",
    "DATABASE_URL": null
  },
  "formation": [
    {"name": "web", "quantity": 2, "size": "standard-1x"},
    {"name": "worker", "quantity": 1, "size": null}
  ],
  "scripts": [
    {"name": "postdeploy", "command": "bundle exec rails db:migrate"}
  ],
  "addons": [
    {"plan": "heroku-postgresql:hobby-dev", "as": null, "options": null}
  ],
  "build_time": 45,
  "language": "ruby",
  "timestamp": "2025-12-18T20:00:00Z"
}

Failure Example

A result file for a failed build:

{
  "status": "failed",
  "exit_code": 1,
  "error": "Docker build failed: npm ERR! Missing: peer dependency react@^18.0.0",
  "images": [],
  "processes": {},
  "build_time": 12,
  "language": "nodejs",
  "timestamp": "2025-12-18T20:01:00Z"
}

Usage

Reading in Shell Scripts

#!/bin/bash
RESULT_FILE="/workspace/output/build-result.json"

# Wait for result file
while [ ! -f "$RESULT_FILE" ]; do sleep 2; done

# Check status
STATUS=$(jq -r '.status' "$RESULT_FILE")
if [ "$STATUS" = "failed" ]; then
  ERROR=$(jq -r '.error' "$RESULT_FILE")
  echo "Build failed: $ERROR"
  exit 1
fi

# Get image name
IMAGE=$(jq -r '.images[0].name' "$RESULT_FILE")
echo "Built image: $IMAGE"

Reading in Python

import json
import time
from pathlib import Path

result_path = Path("/workspace/output/build-result.json")

# Wait for result
while not result_path.exists():
    time.sleep(2)

result = json.loads(result_path.read_text())

if result["status"] == "failed":
    raise Exception(f"Build failed: {result['error']}")

image = result["images"][0]["name"]
ports = result["images"][0]["ports"]
print(f"Built {image} exposing {ports}")

Shipwright Post-Build Step

- name: deploy
  image: your-deployer:latest
  volumeMounts:
    - name: results
      mountPath: /workspace/output
  env:
    - name: RESULT_FILE
      value: /workspace/output/build-result.json

Getting Started

Guides

Configuration

Languages

Deploying

Reference

Overview

Schema

images

processes

env

formation

scripts

addons

_shell

Success Example

Failure Example

Usage

Reading in Shell Scripts

Reading in Python

Shipwright Post-Build Step

​Overview

​Schema

​images

​processes

​env

​formation

​scripts

​addons

​_shell

​Success Example

​Failure Example

​Usage

​Reading in Shell Scripts

​Reading in Python

​Shipwright Post-Build Step

Overview

Schema

images

processes

env

formation

scripts

addons

_shell

Success Example

Failure Example

Usage

Reading in Shell Scripts

Reading in Python

Shipwright Post-Build Step