Delegate_to connection overhead limits during loop execution

Answer the exact question first

1. Connection reuse: When the same delegate_to host is used for every loop iteration, Ansible keeps a single SSH connection open for that host. The connection is established once, cached in the control‑master socket, and reused for each sub‑task in the loop. The connection is closed only when the play finishes or the ControlPersist timeout expires.

2. Limits & recommendations: The reuse is governed by the SSH multiplexing settings in ansible.cfg. If those options are disabled or the ControlPersist timeout is too short, a new connection will be opened for each item. The following settings control the behavior:

• ssh_args = -o ControlMaster=auto -o ControlPersist=60s -o ControlPath=~/.ansible/cp-%h-%p-%r
• pipelining = True (reduces the number of SSH commands per task)
• forks (limits parallel SSH connections)
• Connection plugin ssh (default) or paramiko (does not support multiplexing)

How to verify connection reuse

1. Run the play with -vvv and look for lines like ssh: /usr/bin/ssh -o ControlMaster=auto …. The same ControlPath value should appear for all loop items.
2. Check the ~/.ansible/cp-… socket file – it should exist during the entire loop.
3. Use ss -ltnp | grep ssh while the play runs to see that only one SSH process is active for the delegate host.

Recommended configuration for heavy loops

• Set ControlPersist=300s or higher if the loop takes longer than the default 60 s.
• Use the same host name (not a variable that changes per item) in delegate_to to guarantee the same socket is reused.
• If you must delegate to a different host per item, consider grouping those hosts in the inventory and using delegate_to: hostgroup with a static host name, then filtering inside the task.
• Enable pipelining = True in ansible.cfg to reduce the number of SSH commands per loop iteration.
• Keep forks low enough to avoid exhausting the SSH multiplexing limit (usually 5–10 per host).

When a new connection is still created

• Using the paramiko connection plugin – it does not support ControlPersist.
• Using a different inventory host alias for each loop iteration (e.g., delegate_to: "{{ item.host }}").
• If the SSH socket is removed by an external cleanup script or the system’s temp‑directory is cleaned between iterations.

Ask for missing diagnostic detail

To give a more precise recommendation, could you confirm which connection plugin you are using (default ssh or paramiko) and whether ControlPersist is enabled in your ansible.cfg? This will determine if the connection is truly reused or if a new SSH session is opened for each loop item.