Rollout strategies overview

During the rollout process, Kubernetes creates new pods to replace the existing ones. At the start of the rollout, if the number of pods is near or at capacity, the process can fail because of a lack of resources.

A rollout strategy configures the percentage and number of pods available, so replacement pods are brought up before stopping the pods they replace. This configuration can be set for all new upgrades and deployments, using either the default or custom values.

See more about rolling updates and deployment strategy at Kubernetes API Reference. Hydrolix uses the default strategy from Kubernetes.

Rollout strategies default behavior

By default, the RollingUpdate spec is passed in all deployment types, but only activates if the Kubernetes type is also set to RollingUpdate.

Recreate strategy behavior

For deployments using deployment_strategy="Recreate" and hdx-scaler or Kinesis, the rollout_strategy_max_unavailable and rollout_strategy_max_surge tunables have no effect.

Default rollout values

The default values for Hydrolix are:

• rollout_strategy_max_unavailable: 0
  • Forbids the Kubernetes cluster from stopping and removing any pods until the new pods are ready
• rollout_strategy_max_surge: 25%
  • Allows the Kubernetes cluster to exceed 25% of the replica count as needed

Set custom rollout strategy

The Hydrolix tunables that set the rollout strategy are:

• rollout_strategy_max_unavailable: Defines how many pods can be stopped and removed before new pods are available
• rollout_strategy_max_surge: Defines the percentage of pods that can exceed the replica count as needed

See more about Hydrolix Tunables and how to customize them.