Connection health checks completely ineffective for TLS connections

[nanyan0312]

This is to report a bug in the health check logic for TLS connections. Specifically, in the connCheck function in the internal/pool/conn_check.go file here. It leads to unintentional exhaustions of retry count and ultimately command failures, in the presence of server-side disconnections.

go-redis with non-TLS does not have this problem.

Expected Behavior

The intended use case of connection health check, when picking connections from pool, a health check is made. Bad connections are thrown away immediately. The code keeps picking until a good connection is found. If all pooled connections are bad, a new connection is made. Throwing away a bad connection does not consume retry count. Only when a error happened when using a picked connection to send a command, that error would consume a retry count to be retried.

Current Behavior

The specific bug is, when using TLS, the input argument of the connCheck function is of tls.Conn type. tls.Conn type does not implement the syscall.Conn interface. As result, the type conversion here always returns ok being false therefore bypassing connection health check entirely for TLS connections. Bad connections in the connection pool are used to send commands, resulting in errors. Every bad connection consumes a retry count.

Possible Solution

Steps to Reproduce

1. Set up client to use TLS. With 20 pool size, and 4 retry count. But this issue will be exposed as long as the retry count is lower than the pool size.

        rdb := redis.NewClusterClient(&redis.ClusterOptions{
                Addrs:        []string{""},
                Password:     "",
                PoolSize:     20,
                PoolFIFO:     false,
                MinIdleConns: 10,

                MaxRetries:      4,
                MinRetryBackoff: 8 * time.Millisecond,
                MaxRetryBackoff: 512 * time.Millisecond,

                TLSConfig: &tls.Config{
                        InsecureSkipVerify: true,
                        ServerName:         "you domain",
                },

        })

2. Use client kill type normal on Redis to kill all existing connections all at once.
3. Observe commands failures on client side.

Context (Environment)

Many cloud services hosting Redis offers managed replacements of instances, during which connections on the old instance are killed in batch. Due to this bug, it results in commands failures for TLS clusters, but not non-TLS clusters.