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Percentage rollouts

Percentage rollouts express batches as fractions of the target group instead of fixed counts. They scale gracefully from 50-agent groups to 50 000-agent groups.

When to use

  • The target group will grow or shrink over the life of the rollout (autoscaling, dynamic groups).
  • You want consistent risk exposure across rollouts of different group sizes.
  • You want to leave the operator-cognitive-load level low — "20 % is 20 %" is easier than "27 of 134 means 20 %".

Configuring

In the rollout wizard:

  • Strategy: Percentage.
  • Steps: a list of percentages (5, 25, 50, 100 is the default). The last step must be 100.
  • Auto-advance: off, or on with a dwell timer.

Behaviour

  1. Step 1 (e.g. 5 %) computes the agent count from the current group size at the moment the step starts. If new agents join the group mid-step, they are not added to the in-flight batch.
  2. Each step proceeds like a batch — push, wait for Applied, gate if anything goes wrong.
  3. Steps move forward to the next on advance or auto-advance.

Re-evaluation between steps

Each step re-reads the group's membership at start-of-step. If the group grew between steps 1 and 2, step 2 covers the cumulative N % of the new total (minus the agents already covered).

This re-evaluation matters for dynamic groups: a label change that adds agents during a rollout is naturally absorbed.

Random vs deterministic ordering

By default, agents are randomised within a step — different rollouts on the same group hit different agents first. For repeatability you can pick by host name or by last seen.

A host name ordering plus the same step list across two configurations means "the same agents get the new behaviour first both times" — useful for aligning rollouts on the same canary cohort.

Compared to batch

  • Batch is N agents per batch — easy to reason about for small fleets.
  • Percentage is N % of the group — easy to reason about for large fleets.

Both share the underlying state machine and gates.

Tips

  • The default 5, 25, 50, 100 is a sensible starting point. For high-risk changes, prefer 1, 5, 25, 100 and bias dwell time on the early steps.
  • Percentage rollouts and dynamic groups compose well — let the selector pick the cohort, let the percentages pace the rollout.