Check Ansible Version

As soon as the ansible container are seen in the docker ps command, we should be able to connect to the Ansible container using our definition from the previous step:

a

Let us verify the Ansible installation by running the command:

ansible --version

The output should look similar to:

ansible 2.3.0.0
  config file = /etc/ansible/ansible.cfg
  configured module search path = Default w/o overrides
  python version = 2.7.6 (default, Oct 26 2016, 20:30:19) [GCC 4.8.4]

Check Local Execution

We now can "ping" our local machine:

ansible all -i 'localhost,' -c local -m ping

Note that an ansible ping is not an ICMP request, as you might expect. Instead, it is a test of the SSH connection. However, above we have used an Ansible command with -c local option. This option tells Ansible to bypass the network, so the Ansible client can execute local commands without the need of any SSH connection.

Check Remote Connections

The same Ansible ping will fail, if run it without the -c local flag:

ansible all -i 'localhost,' -m ping

This will lead to following error:

 localhost | UNREACHABLE! => {
    "changed": false,
    "msg": "Failed to connect to the host via ssh: ssh: connect to host localhost port 22: Connection refused\r\n",
    "unreachable": true
}

The same will occur, when wir specify our remote target instead of 'localhost ...

ansible all -i 'target,' -m ping

...and accept the SSH fingerprint with yes

We will resolve this issue during the next steps.

Now try the same Ansible ping without -c local option, forcing Ansible to connect via SSH.

Let us check the status of the SSH service first: service ssh status

If it is not up and running, let us install and start an SSH server: apt-get update; apt-get install -y openssh-server;service ssh start

service ssh status

Now we try to connect to localhost using ansible ansible all -i 'localhost,' -m ping

Accept the fingerprint by typing yes.

We get an error message: Permission denied (publickey,password).

The reason gets clearer, when we try to ssh to the localhost:

ssh localhost

The system is asking for a root password. Instead of allowing users to log in with username and password, we will create and deploy a SSH key pair to source and target in the next step.

Let us generate a SSH key pair like follows: ssh-keygen -t rsa

Now we will add the public key to the list of authorized keys of the ansible host:

cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys

Let us try again to connect to localhost via SSH using Ansible: ansible all -i 'localhost,' -m ping

This time it should work.

Now open a new terminal by clicking on the + sign right of the Terminal tab (otherwise, the next command will not work).

In the second terminal, we run a separate Docker container. This will be our target system.

cd shared_volume && docker run -it --name target --rm --link ansible -v $(pwd):/shared_volume ubuntu:14.04 bash

On the target system, we install and start a SSH Server:

apt-get update; apt-get install -y openssh-server;service ssh start

On the ansible system, let us generate a SSH key pair like follows: ssh-keygen -t rsa

Just keep the defaults and press return three times.

Now we will add the public key of the ansible host to the list of authorized keys of the target host. For that, we make use of a shared_volume between Docker host and the two Docker containers:

cp ~/.ssh/id_rsa.pub /shared_volume/ansible_id_rsa.pub

The public SSH key needs to be appended to the list of ansible's

mkdir ~/.ssh; cat /shared_volume/ansible_id_rsa.pub >> ~/.ssh/authorized_keys

Now let us try to connect to localhost via SSH using Ansible: ansible all -i 'target,' -m ping

This time it should work.

Now let us define the commands "a" and "t" for quickly connecting to the ansible and target container:

Connect to the Ansible container:

a() { 
    docker exec -it ansible bash -c "echo 'PS1='\''ansible# '\' >> /root/.bashrc; bash"; 
}

Connect to the Target container:

t() { 
    docker exec -it target bash -c "echo 'PS1='\''target# '\' >> /root/.bashrc; bash"; 
}

We already have started an ansible and a target container in the background. However, it sometimes takes some time to be available. Use a docker ps command to check, whether Docker containers named 'ansible' and 'target' have been started already:

docker ps

As soon as the containers are available, we should be able to connect to the Ansible container: a

Let us exit from the ansible container

exit

and enter the target container:

t

In our case, the target is an Ubuntu machine with no SSH server installed. Let us do that now:

apt-get update; apt-get install -y openssh-server;service ssh start

In order to be able to connect from the Ansible container to the target container, we need to create a private + public SSH key pair on Ansible and copy the public key to the target machine.

For that, let us exit from the target container

exit

and enter the ansible container again.

a

On the ansible system, let us generate a SSH key pair like follows: ssh-keygen -t rsa

Just keep the defaults, click into the Terminal and press return three times.

This will generate ~/.ssh/id_rsa.pub and ~/.ssh/id_rsa on the ~/.ssh directory:

ls -ltr ~/.ssh

Let us copy the public key of the Ansible host to a shared folder, we have prepared beforehand.

cp ~/.ssh/id_rsa.pub /shared_volume/ansible_id_rsa.pub

In situations, where no shared_volume is available, it is sufficient to copy the content of the file to the clipboard, so we can paste it to the appropriate file on the target.

Append public key to target's authorized_keys file

In order to inform the target about the ansible host's public SSH key, we need to connect to the target again:

exit

t

The public SSH key of the Ansible host needs to be appended to the list of authorized_keys:

[ ! -d ~/.ssh ] && mkdir ~/.ssh; cat /shared_volume/ansible_id_rsa.pub >> ~/.ssh/authorized_keys

Let us review the resulting file:

cat ~/.ssh/authorized_keys

It should contain a line similar to following:

ssh-rsa AAAAB3NzaC1yc2EAA...TtW8ZK5RCND/CR [email protected]

Now, since the target knows about the Ansible host's public SSH key, we are ready to connect from the Ansible host to our target:

exit

a

Now we test the connection, that had failed previously:

ansible all -i 'target,' -m ping

This time we get following output:

target | SUCCESS => {
    "changed": false,
    "ping": "pong"
}

Success!