Idle Connection Timeout Configuration

config/README.md

@@ -40,6 +40,8 @@ max_error_reason_size: <byte_size>
 connection_pool:
   max_idle_conns: 100
   max_idle_conns_per_host: 2
+  # Connection idle timeout must be < Clickhouse `keep_alive_timeout`.
+  idle_conn_timeout: 9
 
 server:
   <server_config> [optional]

config/config.go

@@ -42,6 +42,7 @@ var (
 	defaultConnectionPool = ConnectionPool{
 		MaxIdleConns:        100,
 		MaxIdleConnsPerHost: 2,
+		IdleConnTimeout:     Duration(9 * time.Second),
 	}
 
 	defaultExecutionTime = Duration(120 * time.Second)
@@ -1062,6 +1063,10 @@ type ConnectionPool struct {
 	// Maximum number of idle connections between chproxy and particuler ClickHouse instance
 	MaxIdleConnsPerHost int `yaml:"max_idle_conns_per_host,omitempty"`
 
+	// Time that an idle connection is kept in the pool before being discarded.
+	// Should be set below the ClickHouse server's keep_alive_timeout.
+	IdleConnTimeout Duration `yaml:"idle_conn_timeout,omitempty"`
+
 	// Catches all undefined fields
 	XXX map[string]interface{} `yaml:",inline"`
 }

config/config_test.go

@@ -219,6 +219,7 @@ var fullConfig = Config{
 	ConnectionPool: ConnectionPool{
 		MaxIdleConns:        100,
 		MaxIdleConnsPerHost: 2,
+		IdleConnTimeout:     Duration(9 * time.Second),
 	},
 
 	Users: []User{
@@ -946,6 +947,7 @@ param_groups:
 connection_pool:
   max_idle_conns: 100
   max_idle_conns_per_host: 2
+  idle_conn_timeout: 9s
 `, redisPort)
 	tested := fullConfig.String()
 	if tested != expected {

config/testdata/full.yml

@@ -111,6 +111,10 @@ connection_pool:
   # Number of connections per ClickHouse host to keep open
   # when they are not needed for clients.
   max_idle_conns_per_host: 2
+  # Idle Timeout For Connections To Clickhouse. This value must be < the Clickhouse
+  # `keep_alive_timeout` to prevent graceful disconnection race-conditions that can
+  # result in Bad Gateway (unable to reach host errors)
+  idle_conn_timeout: 9s
 
 # Settings for `chproxy` input interfaces.
 server:

proxy.go

@@ -62,7 +62,7 @@ func newReverseProxy(cfgCp *config.ConnectionPool) *reverseProxy {
 		ForceAttemptHTTP2:     true,
 		MaxIdleConns:          cfgCp.MaxIdleConns,
 		MaxIdleConnsPerHost:   cfgCp.MaxIdleConnsPerHost,
-		IdleConnTimeout:       90 * time.Second,
+		IdleConnTimeout:       time.Duration(cfgCp.IdleConnTimeout),
 		TLSHandshakeTimeout:   10 * time.Second,
 		ExpectContinueTimeout: 1 * time.Second,
 	}