redis: add pub/sub support via RESP3 Push messages

[bellatoris]

Commit Message:

redis: add pub/sub support via RESP3 Push messages

Additional Description:

Follow-up to #44936, which left SUBSCRIBE forwarding as future work. Adds pub/sub to redis_proxy on RESP3 listeners, built on Redis 7 sharded pub/sub: downstream SUBSCRIBE/UNSUBSCRIBE are rewritten upstream to SSUBSCRIBE/SUNSUBSCRIBE, so subscriptions route by cluster slot exactly like keys, and messages reach the client as RESP3 Push frames. A per-worker SubscriptionRegistry owns placement and healing: each channel has one owning upstream host on a dedicated subscription connection, subscribe attempts are generation-tagged and correlated to their out-of-band acks through a per-host FIFO ledger, and upstream connection loss, -MOVED/-ASK on control commands, failover, and slot migration all re-place and re-subscribe with backoff — invisible to the downstream client. Acks are delivered at their position in the request FIFO, pushes never interleave inside pipelined replies, and slow subscribers are bounded by watermark checks plus eviction (the proxy-side analogue of client-output-buffer-limit). Placement is PRIMARY (default) or SHARD_MEMBERS (least-loaded across the shard's primary and replicas); PUBLISH can opt into SPUBLISH rewriting via enable_sharded_publish.

name: envoy.filters.network.redis_proxy
typed_config:
  "@type": type.googleapis.com/envoy.extensions.filters.network.redis_proxy.v3.RedisProxy
  stat_prefix: redis
  protocol_version: RESP3   # pub/sub requires the RESP3 listener mode
  settings:
    op_timeout: 5s
    pubsub_settings: {}     # defaults: 10s ack timeout, 100ms–30s backoff, PRIMARY placement

Design note: sharded-only, deliberately. Classic broadcast pub/sub (SUBSCRIBE fan-out to every node, PSUBSCRIBE patterns) has no slot affinity, so a proxy in front of a cluster cannot place or heal it coherently. PSUBSCRIBE/PUBSUB/RESET remain rejected; the sharded verbs are not client-exposed (and the pub/sub names can no longer be declared in custom_commands); sharded_subscription_mode: DISABLED restores the pre-feature rejection for Redis 6.x upstreams. Separately, commands that fail to queue inside a MULTI (unknown, wrong arity, locally-answered, malformed frames, routing failures) now dirty the transaction so EXEC aborts with -EXECABORT, matching real Redis CLIENT_DIRTY_EXEC semantics — this applies to all listeners and is changelogged.

Risk Level: Medium. Pub/sub is opt-in (protocol_version: RESP3 plus actual subscribe traffic); the RESP2 default path is unchanged. The transaction dirty-EXEC corrections apply to all listeners and are listed in the changelog.

Testing: Unit + integration suites (registry state machine incl. generation/FIFO/topology handling, conn-pool subscription connections, transaction×pubsub boundary, downstream ordering and watermarks). Additionally verified against a real Redis 7.2 cluster (3 primaries + 3 replicas), including subscribe continuity across failover and live slot resharding.

Docs Changes: redis_proxy_filter.rst (pub/sub configuration + new stats), arch overview redis page, API proto docs.

Release Notes: changelogs/current/ — new_features (pub/sub support), minor_behavior_changes (transaction dirty-EXEC), behavior_changes (pub/sub names rejected in custom_commands).

Runtime guard: N/A — feature is config-gated.

Platform Specific Features: N/A

I used generative AI to help author this change.

[repokitteh-read-only]

CC @envoyproxy/api-shepherds: Your approval is needed for changes made to (api/envoy/|docs/root/api-docs/).
envoyproxy/api-shepherds assignee is @adisuissa
CC @envoyproxy/api-watchers: FYI only for changes made to (api/envoy/|docs/root/api-docs/).

🐱

Caused by: #46354 was opened by bellatoris.

see: more, trace.

[repokitteh-read-only]

CC @envoyproxy/coverage-shephards: FYI only for changes made to (test/coverage.yaml).
envoyproxy/coverage-shephards assignee is @RyanTheOptimist

🐱

Caused by: #46354 was synchronize by bellatoris.

see: more, trace.