Docker: change port binding on an already created container with no data loss

Question

Assuming that I have a MongoDb or Sql Server container with a lotta data, and all of a sudden (which is very probable) I need to change the port! Maybe due to a sudden security issue! And I need to stop the container and start it up again running on a different port. Why doesn't docker allow me to do that, if I run the image again a new container will be created with no data inside and that causes a lot of mess.

Is there a proper built-in solution? By proper I mean a solution that does not require me to back up databases, move them to out the container volume and restore them again. Something logical such as a command that can allow me to change the forwarded port, for example -p 1433:1234 to 27017:1234.

Answer 1

BLUF: Start your MongoDB container with a volume mapped in to keep the data persistant using this format: docker run --name some-mongo -v /my/own/datadir:/data/db -d mongo

While I agree, it would be great if Docker had the ability to switch port numbers in a running container. As others said, each container is a process, and I do not know a way of changing a port on a running process.

You do not need to import your data if you have set up your volumes properly. I do this all the time for MySQL databases. The MyQSL image is just the database engine separate from the database if you map in your volumes correctly. That's how Docker is designed.

In looking at the section "Where to store data", it gives an example of mounting a volume to a folder on the host to keep your data. This should allow you to start a new container using the same data without having to re-import. But I'm not as familiar with MongoDB which is a NoSQL.

https://hub.docker.com/_/mongo/#!

You may need backup your database using this dump command:

docker exec some-mongo sh -c 'exec mongodump -d <database_name> --archive' > /some/path/on/your/host/all-collections.archive

Start a new container with the volume mapped and restore the data.

docker run --name some-mongo -v /my/own/datadir:/data/db -v /some/path/on/your/host/all-collections.archive:/data/db/collections.archive -d mongo

You'll need to restore that backup.

docker exec some-mongo sh -c 'exec mongorestore --db <database_name> --archive=/data/db/collections.archive

From that point on you should be able to simply stop and start a new container with the volumes mapped in. Your data should remain persistent. You should not need to dump and restore any more (well, obviously for normal backup purposes).

Answer 2

Container is the instantiation of a image.

The port number is the instantiation state of a container, so it can only be changed while creating a container.