If using for example 'myuser' user but with a custom ssh key name i.e. myuser_github and not id_rsa you will get an error if trying to run the following command:

myuser@host:~/my-user$ git clone git@github.com:someuser/repo.git .  
Cloning into '.'...
Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

Host github.com
	HostName github.com
	User git
    	IdentityFile ~/.ssh/myuser_github

You can use a custom hostname as well, e.g.

Host github-someorg
        HostName github.com
    	IdentityFile ~/.ssh/myuser_github

Then to clone use that host

git clone git@github-someorg:someuser/repo.git

• Clone remote repository with ansible git module using ssh key