Skip to content

Common Operations to initialize a node/service in CentOS infra

Common Operations to initialize a node/service in CentOS infra

Once the server (bare-metal, Virtual Machine - internal or EC2 instance- ) is deployed, we just need to add it to ansible inventory (probably already done already during deploy step so complete with the following information)


  • Machine is reachable
  • You have initial credentials (either already injected ssh key and sudo right or just other equivalent credentials)
  • Access to required Ansible inventory
Adding node

You first need to add the node into DNS (either internally or externally) so please have a look at the dedicated DNS section, and that means kicking the role-bind.yml or role-unbound.yml playbooks based on the need, and after having pushed the change to git.

Once the node is available, we need once to initialize the node to confirm access and ssh host key/fingerprint and then sign it with our SSH CA.

Let's start by first ensuring that we can log onto a node (in our example a EC2 instance):

ssh uptime
The authenticity of host ' (<no hostip for proxy command>)' can't be established.
ECDSA key fingerprint is SHA256:TFnZOT68OAkUQdTm1kCwoPxEN8d/4v/kqinsPcFD/04.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '' (ECDSA) to the list of known hosts.
 09:41:48 up 7 min,  0 users,  load average: 0.00, 0.06, 0.04


it's also possible to not do the ssh host key checking, but not adviced, by using ANSIBLE_HOST_KEY_CHECKING=False env variable in front of the first playbook execution in the next steps. As said, it's possible and should eventually only be used for .dev. or .stg. environment, and on just provisioned instances (non public) like Virtual Machines

Now we can proceed with next steps. Let's add the node in the correct Ansible inventory (like for example CentOS-CI or CentOS-prod or CentOS-staging, etc.

We first need to ensure that usual sysadmins will be granted first the correct rights and we just need to add the node in ansible inventory first. If you already know which roles you want to directly apply feel free to add into correct [group_name] in the inventory or just add it to [unclassified] first. When done, we can just play manually (only once) some playbooks and from there machine will be automatically reconfigured when role/inventory is updated (see the Ansible section about this)

ansible-playbook playbooks/adhoc-grant-access.yml -u centos -l ${fqdn} # or add -k to ask for password if needed to inject ssh keys

Now that sysadmins have their keys injected (including yours), you can initialize the node , but it will create a temporary file that you can then copy into inventory for some gathered facts, so you can use --extras-vars just for this specific call

test -d ${out_dir} || mkdir -p ${out_dir}
ansible-playbook playbooks/adhoc-init-node.yml -l ${fqdn} --extra-vars "out_dir=${out_dir}"
cat ${out_dir}/${fqdn} >> inventory/host_vars/${fqdn}

The adhoc-init-node.yml will do the following :

  • (optional) retrieve the public IP and allow incoming connections from that new ip for some infra services restricted by iptables
  • retrieve ssh host keys, sign these and push the signed
  • retrieve locally some facts that can be used later for basic host_vars template
  • play the baseline role (common for all nodes but with different settings, based on inventory
  • (optional): play other roles that are tied to ansible inventory group membership (if you added the host already in some specific groups)

If you configured correctl

Now that machine is in ansible inventory, you can always add new role, based on group memberships, change settings through group_vars or host_vars, etc, so Ansible BAU


For sponsored nodes, ensure that you define a root password that is unique and set it. Don't forget to reflect it (normally not needed anymore) in ansible/inventory/host_vars/<host> with root_password (all git-crypted and/or ansible-vault crypted depending on the inventory). You can use something like pwgen tool or even just openssl rand -base64 24 (as an example)