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fix: deduplicate consumer groups to prevent scrape failure (#335) #336

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fix: deduplicate consumer groups to prevent scrape failure (#335) #336

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26 changes: 26 additions & 0 deletions prometheus/collect_consumer_groups.go
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,24 @@ func (e *Exporter) collectConsumerGroups(ctx context.Context, ch chan<- promethe

// The list of groups may be incomplete due to group coordinators that might fail to respond. We do log an error
// message in that case (in the kafka request method) and groups will not be included in this list.
//
// seenGroups deduplicates consumer groups to prevent duplicate metric emission.
//
// Root cause: listConsumerGroups calls ListGroups via franz-go, which fans the
// request out to ALL brokers simultaneously (listGroupsSharder → allBrokersShardedReq).
// Each broker responds with the groups it currently believes it coordinates, and
// franz-go merges the responses by simple concatenation. During a coordinator
// migration (common when large consumer groups rebalance), both the old and new
// coordinator broker may transiently include the same group in their ListGroups
// response, producing duplicate group IDs in the merged list.
//
// Those duplicate IDs flow into DescribeGroups, causing the same group to appear
// multiple times in the DescribeGroups response. Without this guard, group-level
// metrics (consumer_group_info, consumer_group_members, …) would be emitted more
// than once per scrape cycle, and the Prometheus registry would reject the entire
// scrape with "collected metric … was collected before with the same name and
// label values".
seenGroups := make(map[string]struct{})
for _, grp := range groups {
coordinator := grp.BrokerMetadata.NodeID
for _, group := range grp.Groups.Groups {
Expand All @@ -37,6 +55,14 @@ func (e *Exporter) collectConsumerGroups(ctx context.Context, ch chan<- promethe
if !e.minionSvc.IsGroupAllowed(group.Group) {
continue
}
if _, seen := seenGroups[group.Group]; seen {
e.logger.Debug("skipping duplicate consumer group from broker shard response",
zap.String("group_id", group.Group),
zap.Int32("broker_id", coordinator),
)
continue
}
seenGroups[group.Group] = struct{}{}
state := 0
if group.State == "Stable" {
state = 1
Expand Down