Compose "Bind for 0.0.0.0:PORT failed: port is already allocated" in CI

Compose tried to publish a service port to the host but the host port is already bound, by a leftover container from a prior job, another compose stack, or a service the runner already runs. The bind fails and the service does not start.

What this error means

A docker compose up fails with "Error response from daemon: driver failed programming external connectivity ... Bind for 0.0.0.0:<port> failed: port is already allocated".

compose

Error response from daemon: driver failed programming external connectivity on
endpoint app_db_1: Bind for 0.0.0.0:5432 failed: port is already allocated

Common causes

A leftover container still holds the port

A previous job did not tear down its stack, so an old container is still bound to the host port.

Another process or stack uses the same host port

A second compose project or a runner service maps the same port, so the second bind is refused.

How to fix it

Tear down old stacks before starting

Run docker compose down (with --remove-orphans) before up.
Use a unique project name per job so stacks do not collide.
Re-run; the port is now free to bind.

Terminal

docker compose down --remove-orphans
docker compose up -d

Let the host port be assigned dynamically

In CI you rarely need a fixed host port; publish to an ephemeral host port to avoid collisions.

docker-compose.yml

services:
  db:
    ports:
      - "5432"   # host port chosen automatically

How to prevent it

Always docker compose down at job start or end.
Use unique project names so stacks do not clash.
Avoid pinning host ports in CI; let Docker assign them.