What postgres connection string on AWS docker multicontainer app? - postgresql

Question

What Postgres connection string should I use if I run a docker multicontainer app via Dockerrun.aws.js on AWS?
I have a Node.JS/Postgres/docker web-application. Postgres runs in its own container and so does the app. Locally, the app runs ok. When I deploy it to AWS via ECR and BeanStalk, the application successfully deploys and runs, but the web-app doesn't connect to Postgres.
In docker-compose.yaml, the host in the connection string is the name of the container (in my case it would be db). That doesn't work with AWS. Neither does localhost or 127.0.0.1.
Here is my Dockerrun.aws.js:
{
"AWSEBDockerrunVersion": 2,
"volumes": [
{
"name": "db-data",
"host": {
"sourcePath": "/data/db"
}
}
],
"containerDefinitions": [
{
"name": "db",
"image": "db_image_name",
"essential": true,
"memory": 128,
"environment": [
{
"name": "POSTGRES_USER",
"value": "postgres"
},
{
"name": "POSTGRES_PASSWORD",
"value": "password"
},
{
"name": "PGDATA",
"value": "/data/db/pgdata"
}
],
"portMappings": [
{
"hostPort": 5432,
"containerPort": 5432
}
],
"mountPoints": [
{
"sourceVolume": "db-data",
"containerPath": "/data/db"
}
]
},
{
"name": "app",
"image": "app_image_name",
"essential": true,
"memory": 128,
"environment": [
{
"name": "NODE_ENV",
"value": "production"
},
{
"name": "DB_HOST",
"value": "db"
},
{
"name": "DB_PORT",
"value": "5432"
},
{
"name": "DB_PASSWORD",
"value": "password"
}
],
"links": [
"db"
],
"portMappings": [
{
"hostPort": 80,
"containerPort": 3000
}
]
}
]
}
What should I put in the environment variable DB_HOST? (DB_HOST together with DB_PORT are used by the app to construct the connection string.) Thanks a lot.

Answer 1

Beanstalk and Dockerrun.aws.json format offer you a possibility to link containers from the same definition file with the following syntax:
"links": ["some-name"]
In your case you can add a link to "db" and postgres will be available in your app container under db. You don't even need to map container ports if you don't want to expose your postgres container to the world.
You can see an example in use in following docs: https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/create_deploy_docker_v2config.html#create_deploy_docker_v2config_dockerrun