No logging or rethrowing on GetReplicasForService in ConnectionMultiplexer

[ThomasTosik]

Hi!

I was trying out the new Sentinel support and had some issues.
Exception thrown: 'System.NullReferenceException' in StackExchange.Redis.dll: 'Object reference not set to an instance of an object.' Stack trace: at StackExchange.Redis.ConnectionMultiplexer.GetSentinelMasterConnection(ConfigurationOptions config, TextWriter log) in /_/src/StackExchange.Redis/ConnectionMultiplexer.cs:line 2401

I started to dig and found out that i had no chance to get to the real issues due to missing logging or rethrowing.

StackExchange.Redis/src/StackExchange.Redis/ConnectionMultiplexer.cs

Line 2530 in f52cba7

catch { return null; }

Is this intentional? After a tedious debug session i got at least my exception that i was looking for...

[mgravell]

"intentional" is complex, but I'm going to assume "probably not", but since the code here is parallel, logging becomes... trickier; what is the scenario that caused this to fail in this way, out of curiosity?

[ThomasTosik]

So the exception that i got was:
Exception thrown: 'StackExchange.Redis.RedisConnectionException' in StackExchange.Redis.dll: 'Unexpected response to SENTINEL: MultiBulk: 0 items' Stack trace: at StackExchange.Redis.ConnectionMultiplexer.ExecuteSyncImpl[T](Message message, ResultProcessor`1 processor, ServerEndPoint server) in /_/src/StackExchange.Redis/ConnectionMultiplexer.cs:line 2826

Some background: I was using the bitnami redis/sentinel setup in my docker tests. I had only one redis master (first naive try). After i added a real redis slave this issue was gone.

[azharmahmood]

Hello, I am getting same error, I have only one remote sentinel master in my test environment. So is the issue resolved by adding a sentinel slave? Please confirm?

[ThomasTosik]

Hello, I am getting same error, I have only one remote sentinel master in my test environment. So is the issue resolved by adding a sentinel slave? Please confirm?

I got it to work with one Sentinel, one Redis Master and one Redis Slave.

[NickCraver]

Thanks for the additional info! The root of the problem here is in SentinelGetSentinelAddressesProcessor I believe, specifically:

StackExchange.Redis/src/StackExchange.Redis/ResultProcessor.cs

Lines 2069 to 2075 in f52cba7

	if (endPoints.Count > 0)
	{
	SetResult(message, endPoints.ToArray());
	return true;
	}
	return false;

The result processor treats "no endpoints" as an invalid state, e.g. in this case where there simply are no replicas. I pushed up a PR for this in #1527.

[NickCraver]

Fixed via #1527