The Redis client throws 'ERR Got an unexpected reply from Redis (node-redis pubsub)' when it receives malformed or unexpected responses during pubsub operations. This usually indicates protocol mismatches between client and server versions, network corruption, or Redis server issues during message publishing. Check client-server compatibility, network stability, and Redis server health to resolve the pubsub communication failures.
When the node-redis client reports "ERR Got an unexpected reply from Redis (node-redis pubsub)", it means the Redis server sent a response that doesn't match the expected Redis protocol format for pubsub operations. Pubsub (publish/subscribe) in Redis uses a specific response pattern where subscribers receive messages as arrays with specific formats. The error typically occurs when: 1. The Redis server sends malformed or corrupted responses 2. There's a protocol version mismatch between client and server 3. Network issues corrupt the TCP packets 4. The Redis server is under heavy load or experiencing issues 5. Client-side parsing fails due to unexpected data types or formats This is a client-side error from the node-redis library, not a server-side Redis error, which means the issue is in the communication layer between your application and Redis.
Verify that your Redis server version is compatible with the node-redis client version:
# Check Redis server version
redis-cli INFO server | grep redis_version
# Check node-redis version in your project
npm list redisCommon compatibility issues:
- Redis 7.x with older node-redis < 4.x
- Redis 6.x with node-redis 4.x (some protocol changes)
- Always check the node-redis documentation for version compatibility matrix
Check for network issues between your application and Redis server:
# Test basic connectivity
ping redis-server-host
# Test Redis connectivity with telnet
telnet redis-server-host 6379
# Type 'PING' and press Enter - should return '+PONG'
# Check for packet loss
mtr redis-server-hostAlso check MTU settings:
# Check current MTU
ip link show | grep mtu
# If using Docker or Kubernetes, check container network settings
docker inspect container_name | grep -i mtuCheck if Redis server is under stress or experiencing issues:
# Check memory usage
redis-cli INFO memory | grep -E '(used_memory|maxmemory|mem_fragmentation_ratio)'
# Check connected clients and pubsub stats
redis-cli INFO clients
redis-cli INFO stats | grep -E '(total_connections_received|rejected_connections|pubsub_channels)'
# Check for slow logs
redis-cli SLOWLOG GET 10
# Monitor Redis in real-time
redis-cli MONITOR | head -50Look for:
- High memory usage (>90% of maxmemory)
- Many connected clients
- Slow commands in slowlog
- Error messages in Redis logs
Update to the latest stable node-redis version and add proper error handling:
# Update node-redis
npm install redis@latestAdd comprehensive error handling in your pubsub code:
const client = createClient({
url: 'redis://localhost:6379',
socket: {
reconnectStrategy: (retries) => {
if (retries > 10) {
console.error('Too many reconnection attempts');
return new Error('Too many retries');
}
return Math.min(retries * 100, 3000);
}
}
});
client.on('error', (err) => {
console.error('Redis client error:', err);
// Implement your error recovery logic here
});
client.on('end', () => {
console.log('Redis client disconnected');
});Create a minimal test to isolate the issue:
// test-pubsub.js
import { createClient } from 'redis';
async function testPubsub() {
const publisher = createClient({ url: 'redis://localhost:6379' });
const subscriber = createClient({ url: 'redis://localhost:6379' });
await publisher.connect();
await subscriber.connect();
// Simple string message
await subscriber.subscribe('test-channel', (message) => {
console.log('Received:', message);
});
await publisher.publish('test-channel', 'simple test message');
await new Promise(resolve => setTimeout(resolve, 1000));
// JSON message
await publisher.publish('test-channel', JSON.stringify({ test: 'data' }));
await new Promise(resolve => setTimeout(resolve, 1000));
await publisher.quit();
await subscriber.quit();
}
testPubsub().catch(console.error);Run this test to see if basic pubsub works. If it fails, the issue is environmental. If it works, compare with your production code to identify differences.
Enable debug logging in node-redis to see the actual protocol exchange:
const client = createClient({
url: 'redis://localhost:6379',
socket: {
tls: false,
}
});
// Enable debug mode
import { commandOptions } from 'redis';
// Or set environment variable
// DEBUG=redis:* node your-app.jsYou can also use Wireshark or tcpdump to capture the actual Redis protocol traffic:
# Capture Redis traffic (adjust interface as needed)
sudo tcpdump -i any port 6379 -w redis-traffic.pcap
# Or use tshark for immediate analysis
sudo tshark -i any -f 'port 6379' -V | grep -A5 -B5 'PUBLISH\|SUBSCRIBE'Look for malformed Redis protocol responses or unexpected data in the captured packets.
The node-redis library (v4+) uses a different protocol parser than earlier versions. If you're migrating from node-redis v3 or earlier, you might encounter this error due to:
1. Different error handling semantics
2. Changed reconnection logic
3. Updated protocol parsing
Consider using Redis' built-in protocol debugging by enabling verbose logging in redis.conf:
loglevel verbose
logfile /var/log/redis/redis-server.logAlso note that Redis Cluster adds another layer of complexity for pubsub - messages are broadcast to all nodes in the cluster, which can cause different failure modes.
For production systems, consider implementing:
1. Circuit breaker pattern for Redis connections
2. Dead letter queues for failed pubsub messages
3. Monitoring for pubsub channel health
4. Automated failover to backup Redis instance
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