Add context/timeout to HTTP throttle check

.golangci.yml

@@ -9,6 +9,8 @@ linters:
   enable:
     - gosimple
     - govet
+    - noctx
     - rowserrcheck
     - sqlclosecheck
     - unused
+

go/base/context.go

@@ -184,7 +184,9 @@ type MigrationContext struct {
 	CurrentLag                             int64
 	currentProgress                        uint64
 	etaNanoseonds                          int64
+	ThrottleHTTPIntervalMillis             int64
 	ThrottleHTTPStatusCode                 int64
+	ThrottleHTTPTimeoutMillis              int64
 	controlReplicasLagResult               mysql.ReplicationLagResult
 	TotalRowsCopied                        int64
 	TotalDMLEventsApplied                  int64

go/cmd/gh-ost/main.go

@@ -1,5 +1,5 @@
 /*
-   Copyright 2016 GitHub Inc.
+   Copyright 2022 GitHub Inc.
 	 See https://github.com/github/gh-ost/blob/master/LICENSE
 */
 
@@ -110,6 +110,8 @@ func main() {
 	throttleControlReplicas := flag.String("throttle-control-replicas", "", "List of replicas on which to check for lag; comma delimited. Example: myhost1.com:3306,myhost2.com,myhost3.com:3307")
 	throttleQuery := flag.String("throttle-query", "", "when given, issued (every second) to check if operation should throttle. Expecting to return zero for no-throttle, >0 for throttle. Query is issued on the migrated server. Make sure this query is lightweight")
 	throttleHTTP := flag.String("throttle-http", "", "when given, gh-ost checks given URL via HEAD request; any response code other than 200 (OK) causes throttling; make sure it has low latency response")
+	flag.Int64Var(&migrationContext.ThrottleHTTPIntervalMillis, "throttle-http-interval-millis", 100, "Number of milliseconds to wait before triggering another HTTP throttle check")
+	flag.Int64Var(&migrationContext.ThrottleHTTPTimeoutMillis, "throttle-http-timeout-millis", 1000, "Number of milliseconds to use as an HTTP throttle check timeout")
 	ignoreHTTPErrors := flag.Bool("ignore-http-errors", false, "ignore HTTP connection errors during throttle check")
 	heartbeatIntervalMillis := flag.Int64("heartbeat-interval-millis", 100, "how frequently would gh-ost inject a heartbeat value")
 	flag.StringVar(&migrationContext.ThrottleFlagFile, "throttle-flag-file", "", "operation pauses when this file exists; hint: use a file that is specific to the table being altered")
@@ -297,7 +299,7 @@ func main() {
 	log.Infof("starting gh-ost %+v", AppVersion)
 	acceptSignals(migrationContext)
 
-	migrator := logic.NewMigrator(migrationContext)
+	migrator := logic.NewMigrator(migrationContext, AppVersion)
 	err := migrator.Migrate()
 	if err != nil {
 		migrator.ExecOnFailureHook()

go/logic/migrator.go

@@ -62,6 +62,7 @@ const (
 
 // Migrator is the main schema migration flow manager.
 type Migrator struct {
+	appVersion       string
 	parser           *sql.AlterTableParser
 	inspector        *Inspector
 	applier          *Applier
@@ -87,8 +88,9 @@ type Migrator struct {
 	finishedMigrating int64
 }
 
-func NewMigrator(context *base.MigrationContext) *Migrator {
+func NewMigrator(context *base.MigrationContext, appVersion string) *Migrator {
 	migrator := &Migrator{
+		appVersion:                 appVersion,
 		migrationContext:           context,
 		parser:                     sql.NewAlterTableParser(),
 		ghostTableMigrated:         make(chan bool),
@@ -1068,7 +1070,7 @@ func (this *Migrator) addDMLEventsListener() error {
 
 // initiateThrottler kicks in the throttling collection and the throttling checks.
 func (this *Migrator) initiateThrottler() error {
-	this.throttler = NewThrottler(this.migrationContext, this.applier, this.inspector)
+	this.throttler = NewThrottler(this.migrationContext, this.applier, this.inspector, this.appVersion)
 
 	go this.throttler.initiateThrottlerCollection(this.firstThrottlingCollected)
 	this.migrationContext.Log.Infof("Waiting for first throttle metrics to be collected")

go/logic/throttler.go

@@ -6,6 +6,7 @@
 package logic
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 	"strings"
@@ -42,16 +43,22 @@ const frenoMagicHint = "freno"
 // Throttler collects metrics related to throttling and makes informed decision
 // whether throttling should take place.
 type Throttler struct {
+	appVersion        string
 	migrationContext  *base.MigrationContext
 	applier           *Applier
+	httpClient        *http.Client
+	httpClientTimeout time.Duration
 	inspector         *Inspector
 	finishedMigrating int64
 }
 
-func NewThrottler(migrationContext *base.MigrationContext, applier *Applier, inspector *Inspector) *Throttler {
+func NewThrottler(migrationContext *base.MigrationContext, applier *Applier, inspector *Inspector, appVersion string) *Throttler {
 	return &Throttler{
+		appVersion:        appVersion,
 		migrationContext:  migrationContext,
 		applier:           applier,
+		httpClient:        &http.Client{},
+		httpClientTimeout: time.Duration(migrationContext.ThrottleHTTPTimeoutMillis) * time.Millisecond,
 		inspector:         inspector,
 		finishedMigrating: 0,
 	}
@@ -285,7 +292,17 @@ func (this *Throttler) collectThrottleHTTPStatus(firstThrottlingCollected chan<-
 		if url == "" {
 			return true, nil
 		}
-		resp, err := http.Head(url)
+
+		ctx, cancel := context.WithTimeout(context.Background(), this.httpClientTimeout)
+		defer cancel()
+
+		req, err := http.NewRequestWithContext(ctx, http.MethodHead, url, nil)
+		if err != nil {
+			return false, err
+		}
+		req.Header.Set("User-Agent", fmt.Sprintf("gh-ost/%s", this.appVersion))
+
+		resp, err := this.httpClient.Do(req)
 		if err != nil {
 			return false, err
 		}
@@ -303,7 +320,8 @@ func (this *Throttler) collectThrottleHTTPStatus(firstThrottlingCollected chan<-
 
 	firstThrottlingCollected <- true
 
-	ticker := time.Tick(100 * time.Millisecond)
+	collectInterval := time.Duration(this.migrationContext.ThrottleHTTPIntervalMillis) * time.Millisecond
+	ticker := time.Tick(collectInterval)
 	for range ticker {
 		if atomic.LoadInt64(&this.finishedMigrating) > 0 {
 			return