在特定端口上运行 Docker 容器

Question

I have a Rails app deployed with Dokku on DigitalOcean. I've created a Postgres database and linked it with a Rails app. Everything worked fine until I restarted the droplet. I figured out that apps stopped working because on restart every Docker container gets a new port and Rails application isn't able to connect to it. If I run dokku postgresql:info myapp it shows the old port, but it has changed. If I manually change database.yml and push it to the dokku repo everything works.

So how do I prevent Docker from assigning different port each time the server restarts? Or maybe there is an option to change ports of running containers.

Answer 1

I don't have much experience with Dokku but for docker there's no such thing of A container's port. In docker you can expose a container's port to receive incoming request and map it to specific ports in your host machine. With that you can, for instance, run your postgres inside a container and tell docker that you wanna expose the 5432, default postgresql port, to receive incoming requests:

sudo docker run --expose=5432 -P <IMAGE> <COMMAND>

The --expose=5432 tells docker to expose the port 5432 to receive incoming connections from outside world. The -P flag tells docker to map all exposed ports in your container to the host machine's port. with that you can connect to postgres pointing to your host's ip:port. If you want to map a container's port to a different host machine port you can use the -p flag:

sudo docker run --expose=5432 -p=666 <IMAGE> <COMMAND>

Not sure if this can help you with Dokku environment, but I hope so. For more information about docker's run command see: https://docs.docker.com/reference/commandline/cli/#run