Support for hot reloading log levels

command/agent/agent.go

@@ -934,10 +934,14 @@ func (a *Agent) ShouldReload(newConfig *Config) (agent, http bool) {
 	a.configLock.Lock()
 	defer a.configLock.Unlock()
 
+	if newConfig.LogLevel != "" && newConfig.LogLevel != a.config.LogLevel {
+		agent = true
+	}
+
 	isEqual, err := a.config.TLSConfig.CertificateInfoIsEqual(newConfig.TLSConfig)
 	if err != nil {
 		a.logger.Error("parsing TLS certificate", "error", err)
-		return false, false
+		return agent, false
 	} else if !isEqual {
 		return true, true
 	}
@@ -962,13 +966,27 @@ func (a *Agent) Reload(newConfig *Config) error {
 	a.configLock.Lock()
 	defer a.configLock.Unlock()
 
-	if newConfig == nil || newConfig.TLSConfig == nil {
+	updatedLogging := newConfig != nil && (newConfig.LogLevel != a.config.LogLevel)
+
+	if newConfig == nil || newConfig.TLSConfig == nil && !updatedLogging {
 		return fmt.Errorf("cannot reload agent with nil configuration")
 	}
 
-	// This is just a TLS configuration reload, we don't need to refresh
-	// existing network connections
+	if updatedLogging {
+		a.config.LogLevel = newConfig.LogLevel
+		a.logger.SetLevel(log.LevelFromString(newConfig.LogLevel))
+	}
+
+	fullUpdateTLSConfig := func() {
+		// Completely reload the agent's TLS configuration (moving from non-TLS to
+		// TLS, or vice versa)
+		// This does not handle errors in loading the new TLS configuration
+		a.config.TLSConfig = newConfig.TLSConfig.Copy()
+	}
+
 	if !a.config.TLSConfig.IsEmpty() && !newConfig.TLSConfig.IsEmpty() {
+		// This is just a TLS configuration reload, we don't need to refresh
+		// existing network connections
 
 		// Reload the certificates on the keyloader and on success store the
 		// updated TLS config. It is important to reuse the same keyloader
@@ -983,17 +1001,12 @@ func (a *Agent) Reload(newConfig *Config) error {
 		a.config.TLSConfig = newConfig.TLSConfig
 		a.config.TLSConfig.KeyLoader = keyloader
 		return nil
-	}
-
-	// Completely reload the agent's TLS configuration (moving from non-TLS to
-	// TLS, or vice versa)
-	// This does not handle errors in loading the new TLS configuration
-	a.config.TLSConfig = newConfig.TLSConfig.Copy()
-
-	if newConfig.TLSConfig.IsEmpty() {
+	} else if newConfig.TLSConfig.IsEmpty() && !a.config.TLSConfig.IsEmpty() {
 		a.logger.Warn("downgrading agent's existing TLS configuration to plaintext")
-	} else {
+		fullUpdateTLSConfig()
+	} else if !newConfig.TLSConfig.IsEmpty() && a.config.TLSConfig.IsEmpty() {
 		a.logger.Info("upgrading from plaintext configuration to TLS")
+		fullUpdateTLSConfig()
 	}
 
 	return nil

command/agent/agent_test.go

@@ -441,6 +441,28 @@ func TestAgent_HTTPCheckPath(t *testing.T) {
 	}
 }
 
+// Here we validate that log levels get updated when the configuration is
+// reloaded. I can't find a good way to fetch this from the logger itself, so
+// we pull it only from the agents configuration struct, not the logger.
+func TestAgent_Reload_LogLevel(t *testing.T) {
+	t.Parallel()
+	assert := assert.New(t)
+
+	agent := NewTestAgent(t, t.Name(), func(c *Config) {
+		c.LogLevel = "INFO"
+	})
+	defer agent.Shutdown()
+
+	assert.Equal("INFO", agent.GetConfig().LogLevel)
+
+	newConfig := &Config{
+		LogLevel: "TRACE",
+	}
+
+	assert.Nil(agent.Reload(newConfig))
+	assert.Equal("TRACE", agent.GetConfig().LogLevel)
+}
+
 // This test asserts that the keyloader embedded in the TLS config is shared
 // across the Agent, Server, and Client. This is essential for certificate
 // reloading to work.

command/agent/log_levels.go

@@ -10,7 +10,7 @@ import (
 // levels that we use.
 func LevelFilter() *logutils.LevelFilter {
 	return &logutils.LevelFilter{
-		Levels:   []logutils.LogLevel{"TRACE", "DEBUG", "INFO", "WARN", "ERR"},
+		Levels:   []logutils.LogLevel{"TRACE", "DEBUG", "INFO", "WARN", "ERROR"},
 		MinLevel: "INFO",
 		Writer:   ioutil.Discard,
 	}