constraints.md

Defining memory contraints for each container is a the best practice as it allows to have more control on over application. This could prevent resources exhaustion in the case a container start acting strangely allocating too much memory.

Acorn offers a way to specify memory constraints using the memory property in the definition of a container. For instance, we can specify the worker container cannot use more than 32Mi of memory:

  worker: {
    build: "./worker/go"
    env: {
     "POSTGRES_USER": "secret://db-creds/username"
     "POSTGRES_PASSWORD": "secret://db-creds/password"
    }
    memory: 32Mi
  }

Note: the amount of memory used here is arbitrary, in a real world scenario we would first observe how the application behaves with time (for instance using a monitoring stack based on Prometheus) and set the memory contraint accordingly.

Memory constraints can also be provided when running an acorn:

acorn run -n vote -m worker=32Mi .

Setup the same memory contraints of 32Mi to all the containers of the VotingApp (voteui, vote, worker, result, resultui, redis and pg) and run the application:

acorn run -n vote --update .

Listing the containers you should see a couple of them (result and vote and probably db are not running correctly)

acorn containers

Under the hood we could see those containers get an OOMKilled error because they reach the memory limit.

To make sure each container have enough resource, change the value of the memory property to 128Mi for all the containers. Once you have tested that the application is running fine you can remove the app and all the related resources:

acorn rm vote --all --force

Acornfile you should have at the end of this step...

containers: {
  voteui: {
    build: "./vote-ui"
    ports: publish : "80/http"
    memory: 128Mi
  }
  vote: {
    build: "./vote"
    ports: "5000/http"
    memory: 128Mi
  }
  redis: {
    image: "redis:7.0.5-alpine3.16"
    ports: "6379/tcp"
    dirs: {
      "/data": "volume://redis"
    }
    memory: 128Mi
  }
  worker: {
    build: "./worker/go"
    env: {
     "POSTGRES_USER": "secret://db-creds/username"
     "POSTGRES_PASSWORD": "secret://db-creds/password"
    }
    memory: 128Mi
  }
  db: {
    image: "postgres:15.0-alpine3.16"
    ports: "5432/tcp"
    env: {
     "POSTGRES_USER": "secret://db-creds/username"
     "POSTGRES_PASSWORD": "secret://db-creds/password"
     "PGDATA": "/var/lib/postgresql/data/db"
    }
    dirs: {
      "/var/lib/postgresql/data": "volume://db"
    }
    memory: 128Mi
  }
  result: {
    build: "./result"
    ports: "5000/http"
    env: {
     "POSTGRES_USER": "secret://db-creds/username"
     "POSTGRES_PASSWORD": "secret://db-creds/password"
    }
    memory: 128Mi
  }
  resultui: {
    build: "./result-ui"
    ports: publish : "80/http"
    memory: 128Mi
  }
}
secrets: {
    "db-creds": {
        type: "basic"
        params: {
          usernameLength:     7
          usernameCharacters: "a-z"
          passwordLength:     10
          passwordCharacters: "A-Za-z0-9"
        }
        data: {
            username: ""
            password: ""
        }
    }
}
volumes: {
    "db": {
        size: 100M
    }
    "redis": {
        size: 100M
    }
}

Note: you can find more information about memory constraints in the Acorn documentation

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