This change enables configuration of http connection pooling

README.md

@@ -73,6 +73,12 @@ It requires a `provided.al2` environment and respects the following env vars:
    `Key=Value,Other=Value` containing the Cloudwatch dimensions to index metrics
    under.
 
+To adjust timeouts, and connection pooling in the HTTP client use the following env vars:
+
+- `BUILDKITE_AGENT_METRICS_TIMEOUT` : Timeout, in seconds, TLS handshake and idle connections, for HTTP requests, to Buildkite API (default 15).
+- `BUILDKITE_AGENT_METRICS_MAX_IDLE_CONNS` : Maximum number of idle (keep-alive) HTTP connections 
+   for Buildkite Agent API. Zero means no limit, -1 disables pooling (default 100).
+
 Additionally, one of the following groups of environment variables must be set
 in order to define how the Lambda function should obtain the required Buildkite
 Agent API token:
@@ -140,43 +146,47 @@ docker run --rm buildkite-agent-metrics -token abc123 -interval 30s -queue my-qu
 $ buildkite-agent-metrics --help
 Usage of buildkite-agent-metrics:
   -backend string
-    	Specify the backend to use: cloudwatch, statsd, prometheus, stackdriver (default "cloudwatch")
+        Specify the backend to use: cloudwatch, newrelic, prometheus, stackdriver, statsd (default "cloudwatch")
   -cloudwatch-dimensions string
-    	Cloudwatch dimensions to index metrics under, in the form of Key=Value, Other=Value
+        Cloudwatch dimensions to index metrics under, in the form of Key=Value, Other=Value
   -cloudwatch-region string
-    	AWS Region to connect to, defaults to $AWS_REGION or us-east-1
+        AWS Region to connect to, defaults to $AWS_REGION or us-east-1
   -debug
-    	Show debug output
+        Show debug output
   -debug-http
-    	Show full http traces
+        Show full http traces
   -dry-run
-    	Whether to only print metrics
+        Whether to only print metrics
   -endpoint string
-    	A custom Buildkite Agent API endpoint (default "https://agent.buildkite.com/v3")
+        A custom Buildkite Agent API endpoint (default "https://agent.buildkite.com/v3")
   -interval duration
-    	Update metrics every interval, rather than once
+        Update metrics every interval, rather than once
+  -max-idle-conns int
+        Maximum number of idle (keep-alive) HTTP connections for Buildkite Agent API. Zero means no limit, -1 disables connection reuse. (default 100)
   -newrelic-app-name string
-    	New Relic application name for metric events
+        New Relic application name for metric events
   -newrelic-license-key string
-    	New Relic license key for publishing events
+        New Relic license key for publishing events
   -prometheus-addr string
-    	Prometheus metrics transport bind address (default ":8080")
+        Prometheus metrics transport bind address (default ":8080")
   -prometheus-path string
-    	Prometheus metrics transport path (default "/metrics")
+        Prometheus metrics transport path (default "/metrics")
   -queue value
-    	Specific queues to process
+        Specific queues to process
   -quiet
-    	Only print errors
+        Only print errors
   -stackdriver-projectid string
-    	Specify Stackdriver Project ID
+        Specify Stackdriver Project ID
   -statsd-host string
-    	Specify the StatsD server (default "127.0.0.1:8125")
+        Specify the StatsD server (default "127.0.0.1:8125")
   -statsd-tags
-    	Whether your StatsD server supports tagging like Datadog
-  -token string
-    	A Buildkite Agent Registration Token
+        Whether your StatsD server supports tagging like Datadog
+  -timeout int
+        Timeout, in seconds, for HTTP requests to Buildkite API (default 15)
+  -token value
+        Buildkite Agent registration tokens. At least one is required. Multiple cluster tokens can be used to gather metrics for multiple clusters.
   -version
-    	Show the version
+        Show the version
 ```
 
 ### Backends

collector/collector.go

@@ -407,18 +407,25 @@ func traceHTTPRequest(req *http.Request) *http.Request {
 	return req
 }
 
-func NewHTTPClient(timeout int) *http.Client {
+func NewHTTPClient(timeout, maxIdleConns int) *http.Client {
 
 	connectionTimeout := time.Duration(timeout) * time.Second
 
 	return &http.Client{
 		Timeout: connectionTimeout,
 		Transport: &http.Transport{
+			MaxIdleConns:          maxIdleConns,
+			IdleConnTimeout:       connectionTimeout,
+			ResponseHeaderTimeout: connectionTimeout,
+			DisableKeepAlives:     false,
 			Dial: (&net.Dialer{
 				Timeout:   connectionTimeout,
 				KeepAlive: connectionTimeout,
 			}).Dial,
 			TLSHandshakeTimeout: connectionTimeout,
 		},
+		CheckRedirect: func(req *http.Request, via []*http.Request) error {
+			return http.ErrUseLastResponse
+		},
 	}
 }

lambda/main.go

@@ -56,6 +56,7 @@ func Handler(ctx context.Context, evt json.RawMessage) (string, error) {
 	quietString := os.Getenv("BUILDKITE_QUIET")
 	quiet := quietString == "1" || quietString == "true"
 	timeout := os.Getenv("BUILDKITE_AGENT_METRICS_TIMEOUT")
+	maxIdleConns := os.Getenv("BUILDKITE_AGENT_METRICS_MAX_IDLE_CONNS")
 
 	debugEnvVar := os.Getenv("BUILDKITE_AGENT_METRICS_DEBUG")
 	debug := debugEnvVar == "1" || debugEnvVar == "true"
@@ -98,13 +99,21 @@ func Handler(ctx context.Context, evt json.RawMessage) (string, error) {
 		timeout = "15"
 	}
 
+	if maxIdleConns == "" {
+		maxIdleConns = "100" // Default to 100 in line with http.DefaultTransport
+	}
+
 	configuredTimeout, err := strconv.Atoi(timeout)
+	if err != nil {
+		return "", err
+	}
 
+	configuredMaxIdleConns, err := strconv.Atoi(maxIdleConns)
 	if err != nil {
 		return "", err
 	}
 
-	httpClient := collector.NewHTTPClient(configuredTimeout)
+	httpClient := collector.NewHTTPClient(configuredTimeout, configuredMaxIdleConns)
 
 	userAgent := fmt.Sprintf("buildkite-agent-metrics/%s buildkite-agent-metrics-lambda", version.Version)
 

main.go

@@ -20,14 +20,15 @@ var metricsBackend backend.Backend
 
 func main() {
 	var (
-		interval    = flag.Duration("interval", 0, "Update metrics every interval, rather than once")
-		showVersion = flag.Bool("version", false, "Show the version")
-		quiet       = flag.Bool("quiet", false, "Only print errors")
-		debug       = flag.Bool("debug", false, "Show debug output")
-		debugHttp   = flag.Bool("debug-http", false, "Show full http traces")
-		dryRun      = flag.Bool("dry-run", false, "Whether to only print metrics")
-		endpoint    = flag.String("endpoint", "https://agent.buildkite.com/v3", "A custom Buildkite Agent API endpoint")
-		timeout     = flag.Int("timeout", 15, "Timeout, in seconds, for HTTP requests to Buildkite API")
+		interval     = flag.Duration("interval", 0, "Update metrics every interval, rather than once")
+		showVersion  = flag.Bool("version", false, "Show the version")
+		quiet        = flag.Bool("quiet", false, "Only print errors")
+		debug        = flag.Bool("debug", false, "Show debug output")
+		debugHttp    = flag.Bool("debug-http", false, "Show full http traces")
+		dryRun       = flag.Bool("dry-run", false, "Whether to only print metrics")
+		endpoint     = flag.String("endpoint", "https://agent.buildkite.com/v3", "A custom Buildkite Agent API endpoint")
+		timeout      = flag.Int("timeout", 15, "Timeout, in seconds, TLS handshake and idle connections, for HTTP requests, to Buildkite API")
+		maxIdleConns = flag.Int("max-idle-conns", 100, "Maximum number of idle (keep-alive) HTTP connections for Buildkite Agent API. Zero means no limit, -1 disables connection reuse.")
 
 		// backend config
 		backendOpt     = flag.String("backend", "cloudwatch", "Specify the backend to use: cloudwatch, newrelic, prometheus, stackdriver, statsd")
@@ -141,7 +142,7 @@ func main() {
 		}
 	}
 
-	httpClient := collector.NewHTTPClient(*timeout)
+	httpClient := collector.NewHTTPClient(*timeout, *maxIdleConns)
 
 	collectors := make([]*collector.Collector, 0, len(tokens))
 	for _, token := range tokens {