feat: warn when multiple trim strategies are specified

Signed-off-by: Eric Jacobson <eric.jacobson@grafana.com>

Author: erj826

pubsub/redis/metadata.yaml

@@ -227,7 +227,10 @@ metadata:
     type: string
   - name: maxLenApprox
     required: false
-    description: Maximum number of items inside a stream. The old entries are automatically evicted when the specified length is reached, so that the stream is left at a constant size. Defaults to unlimited.
+    description: |
+      Maximum number of items inside a stream. The old entries are automatically evicted when the specified length is reached,
+      so that the stream is left at a constant size. Defaults to unlimited.
+      Cannot be used together with streamTTL; only one stream trimming strategy can be active at a time.
     example: "10000"
     type: number
   - name: streamTTL
@@ -237,6 +240,7 @@ metadata:
       This is an approximate value, as it's implemented using Redis stream's MINID trimming with the '~' modifier.
       The actual retention may include slightly more entries than strictly defined by the TTL,
       as Redis optimizes the trimming operation for efficiency by potentially keeping some additional entries.
+      Cannot be used together with maxLenApprox; only one stream trimming strategy can be active at a time.
     example: "30d"
     type: duration
 
@@ -254,4 +258,4 @@ builtinAuthenticationProfiles:
       - name: enableTLS
         required: true
         description: Must be set to true if using EntraID
-        example: "true"
+        example: "true"

pubsub/redis/redis.go

@@ -85,6 +85,10 @@ func (r *redisStreams) Init(ctx context.Context, metadata pubsub.Metadata) error
 	if _, err = r.client.PingResult(ctx); err != nil {
 		return fmt.Errorf("redis streams: error connecting to redis at %s: %s", r.clientSettings.Host, err)
 	}
+
+	if r.clientSettings.MaxLenApprox > 0 && r.clientSettings.StreamTTL > 0 {
+		r.logger.Warn("redis streams: maxLenApprox and streamTTL cannot be used together; only one stream trimming strategy can be active at a time.")
+	}
 	r.queue = make(chan redisMessageWrapper, int(r.clientSettings.QueueDepth)) //nolint:gosec
 
 	for range r.clientSettings.Concurrency {