Is it possible to update a ConnectionMultiplexer with a different connection string, or should it just be recreated?

Question

We're using the StackExchange.Redis client. We are also using Sentinel which tells us when the Redis master changes. Since we've create our connection (as a Lazy<IConnectionMultiplexer> as recommended) we want to know what's the best way to change the connection information to now point to the new Redis master?

We see a few options:

1. When the notification comes from Sentinel, create a new Lazy<IConnectionMultiplexer>
2. Change the connection information on the existing connection multiplexer

Is #2 even possible?

Our current way:

    private Lazy<IConnectionMultiplexer> CreateRedisConnection()
    {
        return new Lazy<IConnectionMultiplexer>(
            () =>
            {
                ConnectionMultiplexer multiplexer = null;

                    //Connect to Sentinel so we can find the redis master
                    ConnectionMultiplexer sentinelMultiplexer = ConnectionMultiplexer.Connect(SentinelOptions);

                    string masterNodeAddress = GetMasterNodeAddress(sentinelMultiplexer);

                    return ConnectionMultiplexer.Connect(masterNode);
            }
        );
    }

And then upon notification, we simply re-call CreateRedisConnection().

But this fully recreates the connection multiplexer vs a more lightweight approach (which might not be possible).

Studer

Answer 1

The recommended approach for handling master changes in StackExchange.Redis with Sentinel is to create a new ConnectionMultiplexer when you detect a change. Recreating the ConnectionMultiplexer is a safer and more straightforward approach compared to trying to modify the existing ConnectionMultiplexer.

If the master changes, creating a new ConnectionMultiplexer allows the library to establish connections to the new master and handle the changes transparently.

Here's a simple modification to your code to illustrate this approach:

private Lazy<IConnectionMultiplexer> redisConnection;

private void InitializeRedisConnection()
{
    redisConnection = new Lazy<IConnectionMultiplexer>(() =>
    {
        // Connect to Sentinel to find the Redis master
        ConnectionMultiplexer sentinelMultiplexer = ConnectionMultiplexer.Connect(SentinelOptions);
        string masterNodeAddress = GetMasterNodeAddress(sentinelMultiplexer);

        // Connect to the Redis master
        return ConnectionMultiplexer.Connect(masterNode);
    });
}

// Call this method when you detect a master change
private void HandleMasterChange()
{
    // Dispose the existing connection, if any
    if (redisConnection?.IsValueCreated == true)
    {
        redisConnection.Value.Dispose();
    }

    // Recreate the connection
    InitializeRedisConnection();
}

In this example, I've added a method HandleMasterChange that disposes of the existing connection if it has been created and then recreates it by calling InitializeRedisConnection. This way, your application can adapt to master changes in Sentinel by recreating the ConnectionMultiplexer when needed.

Recreating the ConnectionMultiplexer is generally considered a cleaner and more reliable approach than attempting to modify an existing one.

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