Since almost everything in Kubernetes is based on label selectors, it has a feature that Docker Swarm doesn’t. We can update multiple Deployments at the same time. We can, for example, issue an update (kubetl set image) that uses filters to find all Mongo databases and upgrade them to a newer release. It is a feature that would require a few lines of bash scripting with Docker Swarm.

However, while the ability to update all Deployments that match specific labels might sound like a useful feature, it often isn’t. More often than not, such actions can produce undesirable effects. If, for example, we have five back-end applications that use Mongo database (one for each), we’d probably want to upgrade them in a more controlled fashion. Teams behind those services would probably want to test each of those upgrades and give their blessings. We probably wouldn’t wait until all are finished, but upgrade a single database when the team in charge of it feels confident.