Add ready command to profilecli (#3497)

Author: bryanhuhta

cmd/profilecli/main.go

@@ -89,6 +89,9 @@ func main() {
 	bucketWebCmd := bucketCmd.Command("web", "Run the web tool for visualizing blocks in object-store buckets.")
 	bucketWebParams := addBucketWebToolParams(bucketWebCmd)
 
+	readyCmd := app.Command("ready", "Check Pyroscope health.")
+	readyParams := addReadyParams(readyCmd)
+
 	// parse command line arguments
 	parsedCmd := kingpin.MustParse(app.Parse(os.Args[1:]))
 
@@ -151,17 +154,26 @@ func main() {
 		if err := blocksCompact(ctx, cfg.blocks.compact.src, cfg.blocks.compact.dst, cfg.blocks.compact.shards); err != nil {
 			os.Exit(checkError(err))
 		}
+	case readyCmd.FullCommand():
+		if err := ready(ctx, readyParams); err != nil {
+			os.Exit(checkError(err))
+		}
 	default:
 		level.Error(logger).Log("msg", "unknown command", "cmd", parsedCmd)
 	}
 }
 
 func checkError(err error) int {
-	if err != nil {
+	switch err {
+	case nil:
+		return 0
+	case notReadyErr:
+		// The reason for the failed ready is already logged, so just exit with
+		// an error code.
+	default:
 		fmt.Fprintf(os.Stderr, "error: %v\n", err)
-		return 1
 	}
-	return 0
+	return 1
 }
 
 type contextKey uint8

cmd/profilecli/ready.go

@@ -0,0 +1,55 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+
+	"github.com/go-kit/log/level"
+	"github.com/pkg/errors"
+)
+
+var (
+	// Occurs when Pyroscope is not ready.
+	notReadyErr = errors.New("not ready")
+)
+
+type readyParams struct {
+	*phlareClient
+}
+
+func addReadyParams(cmd commander) *readyParams {
+	params := &readyParams{}
+	params.phlareClient = addPhlareClient(cmd)
+
+	return params
+}
+
+func ready(ctx context.Context, params *readyParams) error {
+	req, err := http.NewRequest("GET", fmt.Sprintf("%s/ready", params.URL), nil)
+	if err != nil {
+		return err
+	}
+	req = req.WithContext(ctx)
+
+	client := params.phlareClient.httpClient()
+	res, err := client.Do(req)
+	if err != nil {
+		return err
+	}
+	defer res.Body.Close()
+
+	bytes, err := io.ReadAll(res.Body)
+	if err != nil {
+		return err
+	}
+
+	if res.StatusCode != http.StatusOK {
+		level.Error(logger).Log("msg", "not ready", "status", res.Status, "body", string(bytes))
+		return notReadyErr
+	}
+
+	level.Info(logger).Log("msg", "ready")
+	return nil
+}