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app-compose

Debug

In this section, you will learn how to debug container behavior in app-compose.

You will see how to:

  • Track the container startup process to understand what’s happening.
  • Identify why more or fewer containers started than expected.

This will help you quickly find and fix issues in your app.

Container Startup Process

const hireChef = () => ({
  hasBreak: false,
  makePizza: (_: { ingredients: string[] }) => 'pizza',
});
const orderIngredients = () => ['dough', 'sauce', 'cheese'];


const chef = createContainer({
  id: 'John Doe',
  domain: 'italian-chef',
  start: async () => {
    const hiredChef = await hireChef();


    return { api: hiredChef };
  },
});


const ingredients = createContainer({
  id: 'ingredients',
  domain: 'shop',
  dependencies: [chef],
  enable: (api) => api['John Doe'].hasBreak === false,
  start: async () => {
    const orderedIngredients = await orderIngredients();


    return { api: { orderedIngredients } };
  },
});


const pizza = createContainer({
  id: 'pizza',
  domain: 'dish',
  dependencies: [chef, ingredients],
  start: (api) => {
    const pepperoniPizza = api['John Doe'].makePizza({
      ingredients: api.ingredients.orderedIngredients,
    });


    return { api: { pizza: pepperoniPizza } };
  },
});


const cmd = await compose({
  stages: [
    ['prepare', [chef, ingredients]],
    ['cooking', [pizza]],
  ],
  required: 'all',
});


await cmd.up({ debug: true });

When you run this code, you should see the following output in the console:

Terminal window
>> prepare
• John Doe = idle
• ingredients = idle
>> prepare
• John Doe = pending
• ingredients = idle
>> prepare
• John Doe = done
• ingredients = idle
>> prepare
• John Doe = done
• ingredients = pending
>> prepare
• John Doe = done
• ingredients = done
>> cooking
• pizza = idle
>> cooking
• pizza = pending
>> cooking
• pizza = done

Try it

Understanding Why a Container Was Started or Skipped

For this, you can use the diff command, which shows which containers were started, skipped, or added automatically.

const hireChef = () => ({
  hasBreak: false,
  makePizza: (_: { ingredients: string[] }) => 'pizza',
});
const orderIngredients = () => ['dough', 'sauce', 'cheese'];


const chef = createContainer({
  id: 'John Doe',
  domain: 'italian-chef',
  start: async () => {
    const hiredChef = await hireChef();


    return { api: hiredChef };
  },
});


const ingredients = createContainer({
  id: 'ingredients',
  domain: 'shop',


  dependencies: [chef],
  enable: (api) => api['John Doe'].hasBreak === false,
  start: async () => {
    const orderedIngredients = await orderIngredients();


    return { api: { orderedIngredients } };
  },
});


const olives = createContainer({
  id: 'olives',
  domain: 'ingredients',
  start: () => ({ api: { value: 'olives' } }),
});


const pizza = createContainer({
  id: 'pizza',
  domain: 'dish',
  dependencies: [chef, ingredients],
  optionalDependencies: [olives],
  start: (api) => {
    const pepperoniPizza = api['John Doe'].makePizza({
      ingredients: api.ingredients.orderedIngredients,
    });


    return { api: { pizza: pepperoniPizza } };
  },
});


const cmd = await compose({
  stages: [
    ['prepare', [ingredients]],
    ['cooking', [pizza]],
  ],
  required: 'all',
});


await cmd.diff();

When you run this code, you should see the following highlighted output in the console:

Terminal window
[app-compose] | diff command
All skipped containers are optional. If they are expected to work,
please include them in the list when calling `compose` function


Stages:
- prepare:
    expected: [ ingredients ]
    received: [ ingredients, John Doe ]
- cooking:
    expected: [ pizza ]
    received: [ pizza ]
    skipped:
            - olives: [pizza]

Try it