Chapter 11

1. Zero downtime means that when updating a service, say from version 1 to version 2, the application to which this service belongs remains up and running all the time. At no time is the application interrupted or not functional.
2. Docker SwarmKit uses rolling updates to achieve zero downtime. Every service runs in multiple instances for high availability. When a rolling update is happening, small batches of the overall set of service instances are replaced by new versions. This happens while the majority of the service instances are up and running to serve incoming requests.
3. Container images are immutable. That is, once created, they can never be changed. When a containerized application or service needs to be updated, a new container image is created. During a rolling update, the old container image is replaced with the new container image. If a rollback is necessary...