waiting service database running before others services running in Docker [duplicate] - postgresql

Question

This question already has answers here:
Docker Compose wait for container X before starting Y
(20 answers)
Closed 3 years ago.
I am trying to run my app which depends_on my Postgresql in Docker
let say my database PostgreSQL not running now
and in my docker-compose.yml:
version: "3"
services:
myapp:
depends_on:
- db
container_name: myapp
build:
context: .
dockerfile: Dockerfile
restart: on-failure
ports:
- "8100:8100"
db:
container_name: postgres
restart: on-failure
image: postgres:10-alpine
ports:
- "5555:5432"
environment:
POSTGRES_USER: myuser
POSTGRES_PASSWORD: 12345678
POSTGRES_DB: dev
when I try docker-compose up -d yes it created the postgres and then create that myapp service
but it seems my Postgresql is not running yet, after finish install and running myapp,
it said:
my database server not running yet
how to make myapp running until that db service know that my db running ??

Answer 1

The documentation of depends_on says that:
depends_on does not wait for db to be “ready” before starting myapp - only until it have been started.
So you'll have to check that your database is ready by yourself before running your app.
Docker has a documentation that explains how to write a wrapper script to do that:
#!/bin/sh
# wait-for-postgres.sh
set -e
host="$1"
shift
cmd="$#"
until PGPASSWORD=$POSTGRES_PASSWORD psql -h "$host" -U "postgres" -c '\q'; do
>&2 echo "Postgres is unavailable - sleeping"
sleep 1
done
>&2 echo "Postgres is up - executing command"
exec $cmd
Then you can just call this script before running your app in your docker-compose file:
command: ["./wait-for-postgres.sh", "db", "python", "app.py"]
There are also tools such as wait-for-it, dockerize or wait-for.
However these solutions has some limitations and Docker says that:
The best solution is to perform this check in your application code, both at startup and whenever a connection is lost for any reason.
This method will be more resilient.
Here is how I use a retry strategy in javascript:
async ensureConnection () {
let retries = 5
const interval = 1000
while (retries) {
try {
await this.utils.raw('SELECT \'ensure connection\';')
break
} catch (err) {
console.error(err)
retries--
console.info(`retries left: ${retries}, interval: ${interval} ms`)
if (retries === 0) {
throw err
}
await new Promise(resolve => setTimeout(resolve, interval))
}
}
}

Answer 2

Please have a look at: https://docs.docker.com/compose/startup-order/.
Docker-compose won't wait for your database, you need a way to check it externally (via script or retrying the connection as Mickael B. proposed). One of the solutions proposed in the above link is a wait-for.sh utility script - we used it in a project and it worked quite well.