It seems like

prefect server

is trying to run

docker-compose

inside its own container and not finding the binary?

prefect-server-1  | FileNotFoundError: [Errno 2] No such file or directory: 'docker-compose': 'docker-compose'

This is the compose file I'm using:

---
version: "3.7"

services:
  prefect-server:
    image: prefecthq/prefect
    restart: always
    command: prefect server start
    environment:
      - PREFECT_UI_URL=<http://127.0.0.1:4900/api>
      - PREFECT_API_URL=<http://127.0.0.1:4900/api>
      - PREFECT_SERVER_API_HOST=0.0.0.0
    ports:
      - 4900:4900

Try this one. Make sure you set the environment vars:

services:
  db:
    container_name: db
    image: postgres:${POSTGRES_VERSION}
    restart: unless-stopped
    environment:
      - POSTGRES_USER=${PREFECT_POSTGRES_USER}
      - POSTGRES_PASSWORD=${PREFECT_POSTGRES_PASSWORD}
      - POSTGRES_DB=prefect
    volumes: 
      - db:/var/lib/postgresql/data
    networks:
      - prefect

  prefect:
    container_name: prefect
    image: prefecthq/prefect:${PREFECT_IMAGE}
    restart: unless-stopped
    volumes:
      - prefect:/root/.prefect
    environment:
      - PREFECT_API_URL=<http://127.0.0.1:4200/api>
      - PREFECT_SERVER_API_HOST=0.0.0.0
      - PREFECT_API_DATABASE_CONNECTION_URL=postgresql+asyncpg://${PREFECT_POSTGRES_USER}:${PREFECT_POSTGRES_PASSWORD}@db:5432/prefect
    command: prefect server start
    ports:
      - 4200:4200
    networks:
      - prefect
    depends_on: 
      - db

volumes:
  prefect:
  db:
networks:
  prefect:

Apparently my issue is related to the

latest

tag on Docker hub being more than a year old. This is probably a bit confusing for most users.

When trying to run Prefect Server (specifically running

prefect server start

) in an environment with existing containers, you want to use a

docker-along-side-docker

approach. Basically in your compose file you want to bind mount the host's docker socket into the container that run's the

prefect server start

command. Something like

services:
  prefect-server:
    # ...
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock

This will allow your

prefect-server

container to create sibling containers. Without the bind, the

prefect-server

would create child containers inside of itself (called docker-in-docker). This works, but is actively discouraged by the person who implemented the functionality to allow it. Using the bind mount to the docker socket essentially turns your

prefect-server

into an orchestration or command & control container, similar to how Kubernetes operates. The

prefect-server

container needs to have

docker-compose

installed and accessible, but does not need to have

docker

installed. The only other change needed is to adjust the host name of the Prefect API server. Since everything is running inside Docker and over a bridge network, container's cannot refer to other containers using

localhost

Instead they must use the name of the service. The command

prefect server start

will create several services, one of them named

appollo

, That is the API server. To get the other services to use it, you just need to create the following configuration file:

backend = "server"

[server]
# "apollo" is the name of the prefect/docker-compose service that runs the Prefect server. Any container that uses this
# config file must be on the same docker network as the Prefect server (default: prefect-server)
host = "<http://apollo>"
port = "4200"