Glossary

Rolling Update

Rolling update is a deployment strategy where a new version is rolled out gradually: instances are updated one at a time or in small batches while the old version continues handling requests. Zero downtime without doubling resources.

Flow

Start:  [v1][v1][v1][v1]

Step 1: [v2][v1][v1][v1]  ← one instance updated
Step 2: [v2][v2][v1][v1]
Step 3: [v2][v2][v2][v1]
End:    [v2][v2][v2][v2]

Parameters

maxUnavailable — how many instances may be unavailable simultaneously
maxSurge — how many extra instances above the desired count are allowed

Version compatibility problem

During a rolling update, v1 and v2 run simultaneously. If v2 changed the DB schema, v1 may not understand the new data. Solutions: backward-compatible migrations or feature flags.

Vs Blue-Green, Canary

Rolling update is the most resource-efficient option (no extra resources needed). Blue-Green requires double the resources. Canary offers finer-grained traffic control.