Redis Stream consumer groups: reliable message processing with XACK

Consumer groups for reliable processing

Consumer groups let multiple workers share stream processing, with each message delivered to exactly one worker. Unacknowledged messages stay in a pending entries list (PEL) so they can be reclaimed if a worker fails.

Setup and consuming

# Create a group starting from the beginning of the stream
XGROUP CREATE events workers $ MKSTREAM

# Worker reads up to 10 undelivered messages
XREADGROUP GROUP workers consumer1 COUNT 10 STREAMS events >
# '>' means: give me messages not yet delivered to any consumer

Acknowledging

# After processing, acknowledge the entry ID
XACK events workers 1700000000000-0

Recovering stuck messages

# List messages pending longer than 60 seconds
XPENDING events workers - + 10

# Claim them for another consumer
XCLAIM events workers consumer2 60000 1700000000000-0

Without XACK, the message stays in the PEL. XCLAIM transfers ownership to a healthy consumer, ensuring at-least-once delivery. Design your consumers to be idempotent — the same message may be processed more than once if a worker crashes after processing but before ACKing.