testing ssh key on host works fine but not in container with same keys

I have some ssh keys I use with github. Per this page, I tested them locally:

ssh -T git@github.com
Hi doug-companyname! You've successfully authenticated, but GitHub does not provide shell access.

I'm running a docker-container and under volumes in docker-compose I have:

- ~/.ssh:/home/rstudio/.ssh

This is to give the container the same keys as local.

When I run the container if I look in ~/.ssh I do see the keys:

rstudio@9b5b5114115b:~$ ls -l ~/.ssh
total 12
-rw------- 1 1001 1001  452 Nov  7 19:35 id_ed25519
-rw-r--r-- 1 1001 1001  131 Nov  7 19:35 id_ed25519.pub
-rw-r--r-- 1 1001 1001 2212 Nov 15 16:50 known_hosts

These are indeed the same as the hosts, my local. However, when I try to do the same test I get:

rstudio@9b5b5114115b:~$ ssh -T git@github.com
bash: ssh: command not found

Why are my keys not working in my container but they work fine on local?

Solution

I suspect that your image does not have an SSH client installed by default. Add the below line in your Dockerfile.

RUN apk add --no-cache openssh-client