​
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

FieldTypeDescription
status"success" or "failed"Build outcome
exit_codenumberDocker build exit code (0 on success)
errorstringError message (only present on failure)
imagesarrayBuilt images with detected ports
processesobjectProcess types from Procfile
envobjectEnvironment variables from app.json
formationarrayProcess formation from app.json
scriptsarrayDeployment scripts from app.json
build_timenumberBuild duration in seconds
languagestringDetected or specified language
timestampstringISO 8601 build completion time
_shellbooleanfalse 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"}
  ]
}

​
_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"}
  ],
  "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