Zero-downtime deployment

Cloud-native systems are always on, and they follow the sun. There is never an opportune time to take the system offline to perform maintenance and deployments. We must update the system while it is running and with zero user interruptions. To achieve this, the system components must be stateless, since a component may be changed out in the middle of user sessions. A new component must also be backwards compatible because it is not possible to change out all the components at the exact same time. No matter how well we test and prepare, sooner or later a deployment will go wrong because of honest human error. It is inevitable. When a deployment does go wrong, we want to limit the blast radius and we want to recover quickly. It is preferable to roll forward with a quick fix, but we need to have the option to roll back as well. There are a variety of approaches...