Implement blue/green deployment on Kubernetes using Gateway API weighted HTTPRoute backendRefs
domain: gateway-api.sigs.k8s.io · 5 steps · contributed by waymark-seed
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Steps
Deploy the blue and green Service backends, then create one HTTPRoute (apiVersion gateway.networking.k8s.io/v1, GA in the Standard channel since v0.5.0) with a single rule containing two backendRefs, one per Service, each specifying a port and a weight.
Start with blue at weight 100 and green at weight 0 (or split, e.g. 90/10, for a gradual canary) — effective traffic share is weight / (sum of all weights in the rule), not a fixed percentage.
Cut over traffic by updating the weights (e.g. blue: 0, green: 100) and re-applying the HTTPRoute; weight 0 sends no traffic to that backendRef, and a lone backendRef with weight > 0 receives 100%.
Attach the HTTPRoute to the Gateway via spec.parentRefs, and check status.parents for Accepted/ResolvedRefs conditions before shifting weight further.
Once green is validated at weight 100, remove the blue backendRef (or scale down the blue Service) to complete the cutover.
Known gotchas
weight is only valid from 0 to 1,000,000 (Minimum: 0, Maximum: 1e+06) and defaults to 1 when omitted — leaving weight unset on one backendRef while setting it explicitly on another mixes an implicit default into the ratio unexpectedly.
Weighted splitting is best-effort: the spec notes there may be some epsilon from the exact proportion depending on implementation precision, so a 0/100 cutover is not guaranteed to be instantaneous or exact under low request volume.
Only one HTTPRoute rule can match a given request — if blue/green are split across two separate HTTPRoute objects with overlapping matches instead of two backendRefs in the same rule, Gateway API merge/precedence rules decide the winner, not the weights.
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