How a play moves a whole fleet through its tasks, and how you bound the damage when a change is wrong. Strategies and forks, serial batching and rolling deploys, delegation to the load balancer, async for long jobs, and the throttles that stop a push tool from pushing a mistake everywhere at once — assembled into a zero-downtime rollout of the Larkspur prod web tier.
6 topics
Everything before this chapter shaped a single host well. This chapter is about the fleet — how Ansible moves dozens of hosts through one play, in what order, how many at a time, and what happens when host four of six fails. The running example is Larkspur's Layer B: six prod web hosts behind HAProxy on lb1.larkspur.io, staging and prod, the real thing a deploy has to touch without dropping a request.
This is also where the spine of the course pays off. Ansible keeps no state file and pushes changes from a control node rather than waiting for each host to pull — and an ordered, gated, cross-host rollout is exactly what that push model does cleanly and a pull model cannot. The six topics build toward one marquee play: a rolling deploy that drains each web host from the load balancer, deploys it, health-checks it, and returns it to the pool, one host out of service at a time.