How do I SSH from a Docker container to a remote server

Question

I am building a docker image off postgres image, and I would like to seed it with some data.

I am following the initialization-scripts section of the documentation.

But the problem I am facing now, is that my initialisation scripts needs to ssh to a remote database and dumb data from there. Basically something like this:

ssh remote.host "pg_dump -U user -d somedb" > some.sql

but this fails with the error that ssh: command not found

Question now is, in general, how do I ssh from a docker container to a remote server. In this case, specifically how do I ssh from a docker container to a remote database server as part of the initialisation step of seeding a postgres database?

Answer 1

As a general rule you don't do things this way. Typical Docker images contain only the server they're running and some core tools, but network clients like ssh or curl generally aren't part of this. In the particular case of ssh, securely managing the credentials required is also tricky (not impossible, but not obvious).

In your particular case, I might rearrange things so that your scripts didn't have the hard assumption the database was running locally. Provision an empty database container, then run your script from the host targeting that empty database. It may even work to set the PGHOST and PGPORT environment variables to point to your host machine's host name and the port you publish the database interface on, and then run that script unmodified.

Looking closer at that specific command, you also may find it better to set up a cron job to run that specific database dump and put the contents somewhere. Then a developer can get a snapshot of the data without having to make a connection to the live database server, and you can limit the number of people who will have access. Once you have this dump file, you can use the /docker-entrypoint-initdb.d mechanism to cause it to be loaded at first startup time.