command/agent: Google Compute Engine host discovery

command/agent/command_test.go

@@ -331,6 +331,33 @@ func TestDiscoverEC2Hosts(t *testing.T) {
 	}
 }
 
+func TestDiscoverGCEHosts(t *testing.T) {
+	if os.Getenv("GCE_PROJECT") == "" {
+		t.Skip("GCE_PROJECT not set, skipping")
+	}
+
+	if os.Getenv("GOOGLE_APPLICATION_CREDENTIALS") == "" && os.Getenv("GCE_CONFIG_CREDENTIALS") == "" {
+		t.Skip("GOOGLE_APPLICATION_CREDENTIALS or GCE_CONFIG_CREDENTIALS not set, skipping")
+	}
+
+	c := &Config{
+		RetryJoinGCE: RetryJoinGCE{
+			ProjectName:     os.Getenv("GCE_PROJECT"),
+			ZonePattern:     os.Getenv("GCE_ZONE"),
+			TagValue:        "consulrole-server",
+			CredentialsFile: os.Getenv("GCE_CONFIG_CREDENTIALS"),
+		},
+	}
+
+	servers, err := c.discoverGCEHosts(log.New(os.Stderr, "", log.LstdFlags))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(servers) != 3 {
+		t.Fatalf("bad: %v", servers)
+	}
+}
+
 func TestSetupAgent_RPCUnixSocket_FileExists(t *testing.T) {
 	conf := nextConfig()
 	tmpDir, err := ioutil.TempDir("", "consul")

command/agent/config.go

@@ -132,6 +132,31 @@ type RetryJoinEC2 struct {
 	SecretAccessKey string `mapstructure:"secret_access_key"`
 }
 
+// RetryJoinGCE is used to configure discovery of instances via Google Compute
+// Engine's API.
+type RetryJoinGCE struct {
+	// The name of the project the instances reside in.
+	ProjectName string `mapstructure:"project_name"`
+
+	// A regular expression (RE2) pattern for the zones you want to discover the instances in.
+	// Example: us-west1-.*, or us-(?west|east).*.
+	ZonePattern string `mapstructure:"zone_pattern"`
+
+	// The tag value to search for when filtering instances.
+	TagValue string `mapstructure:"tag_value"`
+
+	// A path to a JSON file with the service account credentials necessary to
+	// connect to GCE. If this is not defined, the following chain is respected:
+	// 1. A JSON file whose path is specified by the
+	//		GOOGLE_APPLICATION_CREDENTIALS environment variable.
+	// 2. A JSON file in a location known to the gcloud command-line tool.
+	//    On Windows, this is %APPDATA%/gcloud/application_default_credentials.json.
+	//  	On other systems, $HOME/.config/gcloud/application_default_credentials.json.
+	// 3. On Google Compute Engine, it fetches credentials from the metadata
+	//    server.  (In this final case any provided scopes are ignored.)
+	CredentialsFile string `mapstructure:"credentials_file"`
+}
+
 // Performance is used to tune the performance of Consul's subsystems.
 type Performance struct {
 	// RaftMultiplier is an integer multiplier used to scale Raft timing
@@ -426,6 +451,9 @@ type Config struct {
 	// RetryJoinEC2 configuration
 	RetryJoinEC2 RetryJoinEC2 `mapstructure:"retry_join_ec2"`
 
+	// The config struct for the GCE tag server discovery feature.
+	RetryJoinGCE RetryJoinGCE `mapstructure:"retry_join_gce"`
+
 	// RetryJoinWan is a list of addresses to join -wan with retry enabled.
 	RetryJoinWan []string `mapstructure:"retry_join_wan"`
 
@@ -1446,6 +1474,18 @@ func MergeConfig(a, b *Config) *Config {
 	if b.RetryJoinEC2.TagValue != "" {
 		result.RetryJoinEC2.TagValue = b.RetryJoinEC2.TagValue
 	}
+	if b.RetryJoinGCE.ProjectName != "" {
+		result.RetryJoinGCE.ProjectName = b.RetryJoinGCE.ProjectName
+	}
+	if b.RetryJoinGCE.ZonePattern != "" {
+		result.RetryJoinGCE.ZonePattern = b.RetryJoinGCE.ZonePattern
+	}
+	if b.RetryJoinGCE.TagValue != "" {
+		result.RetryJoinGCE.TagValue = b.RetryJoinGCE.TagValue
+	}
+	if b.RetryJoinGCE.CredentialsFile != "" {
+		result.RetryJoinGCE.CredentialsFile = b.RetryJoinGCE.CredentialsFile
+	}
 	if b.RetryMaxAttemptsWan != 0 {
 		result.RetryMaxAttemptsWan = b.RetryMaxAttemptsWan
 	}

command/agent/config_test.go

@@ -1047,6 +1047,32 @@ func TestRetryJoinEC2(t *testing.T) {
 	}
 }
 
+func TestRetryJoinGCE(t *testing.T) {
+	input := `{"retry_join_gce": {
+	  "project_name": "test-project",
+		"zone_pattern": "us-west1-a",
+		"tag_value": "consul-server",
+		"credentials_file": "/path/to/foo.json"
+	}}`
+	config, err := DecodeConfig(bytes.NewReader([]byte(input)))
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if config.RetryJoinGCE.ProjectName != "test-project" {
+		t.Fatalf("bad: %#v", config)
+	}
+	if config.RetryJoinGCE.ZonePattern != "us-west1-a" {
+		t.Fatalf("bad: %#v", config)
+	}
+	if config.RetryJoinGCE.TagValue != "consul-server" {
+		t.Fatalf("bad: %#v", config)
+	}
+	if config.RetryJoinGCE.CredentialsFile != "/path/to/foo.json" {
+		t.Fatalf("bad: %#v", config)
+	}
+}
+
 func TestDecodeConfig_Performance(t *testing.T) {
 	input := `{"performance": { "raft_multiplier": 3 }}`
 	config, err := DecodeConfig(bytes.NewReader([]byte(input)))