feat: [alb] add concurrency limit options

docs/alb.md

@@ -193,7 +193,7 @@ This mechanism is useful in applications such as live internet television. Consi
 
 #### Custom Good Status Codes List
 
-By default, fgr will return the first response with a status code < 400. However, you can optionally provide an explicit list of good status codes using the `fgr_status_codes` configuration setting, as shown in the example below. When set, Trickster will return the first response to be returned that has a status code found in the configured list.
+By default, fgr will return the first response with a status code < 400. However, you can optionally provide an explicit list of good status codes using the `fgr.status_codes` configuration setting, as shown in the example below. When set, Trickster will return the first response to be returned that has a status code found in the configured list.
 
 #### First Good Response Configuration Example
 
@@ -216,10 +216,11 @@ backends:
     provider: alb
     alb:
       mechanism: fgr # first good response
-      fgr_status_codes: [ 200, 201, 204 ] # only consider these codes when selecting a response
       pool:
         - node01
         - node02
+      fgr:
+        status_codes: [ 200, 201, 204 ] # only consider these codes when selecting a response
 ```
 
 Here is the visual representation of this configuration:

examples/conf/example.full.yaml

@@ -557,11 +557,11 @@ backends:
 #       # -1 includes all backends, regardless of reporting state
 #       # default is 0
 #       healthy_floor: 0
-
-#       # fgr_status_codes is a list of status codes considered 'good' when using the fgr mechanism
-#       # when this is not set, any response code < 400 is considered good. Use this setting to
-#       # provide an explicit list.
-#       fgr_status_codes: [ 200 ] # this would consider only 200 OK's good, and not 204, 302, etc.
+#       fgr: # First Good Response mechanism options, only applicable when mechanism is set to fgr
+#         # status_codes is a list of status codes considered 'good' when using the fgr mechanism
+#         # when this is not set, any response code < 400 is considered good. Use this setting to
+#         # provide an explicit list.
+#         status_codes: [ 200 ] # this would consider only 200 OK's good, and not 204, 302, etc.
 
 # # Configuration Options for Request Routing Rules - see /docs/rule.md for more information
 

pkg/backends/alb/alb_502_test.go

@@ -23,7 +23,6 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/require"
-
 	"github.com/trickstercache/trickster/v2/pkg/backends/alb/mech/tsm"
 	"github.com/trickstercache/trickster/v2/pkg/backends/alb/names"
 	ao "github.com/trickstercache/trickster/v2/pkg/backends/alb/options"

pkg/backends/alb/mech/fr/first_response.go

@@ -19,7 +19,6 @@ package fr
 import (
 	"context"
 	"net/http"
-	"sync"
 	"sync/atomic"
 
 	"github.com/trickstercache/trickster/v2/pkg/backends/alb/mech/types"
@@ -32,6 +31,7 @@ import (
 	"github.com/trickstercache/trickster/v2/pkg/proxy/request"
 	"github.com/trickstercache/trickster/v2/pkg/proxy/response/capture"
 	"github.com/trickstercache/trickster/v2/pkg/util/sets"
+	"golang.org/x/sync/errgroup"
 )
 
 const (
@@ -46,6 +46,7 @@ type handler struct {
 	pool     pool.Pool
 	fgr      bool
 	fgrCodes sets.Set[int]
+	options  options.FirstGoodResponseOptions
 }
 
 func RegistryEntry() types.RegistryEntry {
@@ -60,6 +61,7 @@ func NewFGR(o *options.Options, _ rt.Lookup) (types.Mechanism, error) {
 	return &handler{
 		fgr:      true,
 		fgrCodes: o.FgrCodesLookup,
+		options:  o.FGROptions,
 	}, nil
 }
 
@@ -109,13 +111,11 @@ func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 	// otherwise iterate the fanout
 	var claimed int64 = -1
-	contexts := make([]context.Context, l)
-	cancels := make([]context.CancelFunc, l)
-	for i := range l {
-		contexts[i], cancels[i] = context.WithCancel(r.Context())
-	}
 	captures := make([]*capture.CaptureResponseWriter, l)
-	var wg sync.WaitGroup
+	var eg errgroup.Group
+	if limit := h.options.ConcurrencyOptions.GetQueryConcurrencyLimit(); limit > 0 {
+		eg.SetLimit(limit)
+	}
 	responseWritten := make(chan struct{}, 1)
 
 	serve := func(crw *capture.CaptureResponseWriter) {
@@ -126,47 +126,37 @@ func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		responseWritten <- struct{}{}
 	}
 
-	serveAndCancelOthers := func(i int, crw *capture.CaptureResponseWriter) {
-		go func() {
-			// cancels all other contexts
-			for j, cancel := range cancels {
-				if j != i {
-					cancel()
-				}
-			}
-		}()
-		serve(crw)
-	}
-
 	// fanout to all healthy targets
+	ctx, cancel := context.WithCancel(r.Context())
+	defer cancel()
 	for i := range l {
 		if hl[i] == nil {
 			continue
 		}
-		wg.Go(func() {
+		eg.Go(func() error {
 			r2, _ := request.Clone(r)
-			r2 = r2.WithContext(contexts[i])
+			r2 = r2.WithContext(ctx)
 			r2 = request.SetResources(r2, &request.Resources{Cancelable: true})
 			crw := capture.NewCaptureResponseWriter()
 			captures[i] = crw
 			hl[i].ServeHTTP(crw, r2)
 			statusCode := crw.StatusCode()
 			custom := h.fgr && len(h.fgrCodes) > 0
 			isGood := custom && h.fgrCodes.Contains(statusCode)
-			// this checks if the response qualifies as a client response
-			if (!h.fgr || (!custom && statusCode < 400) || isGood) &&
-				// this checks that the qualifying response is the first response
-				atomic.CompareAndSwapInt64(&claimed, -1, int64(i)) {
-				// this serves only the first qualifying response
-				serveAndCancelOthers(i, crw)
+
+			if (!h.fgr || (!custom && statusCode < 400) || isGood) && // this checks if the response qualifies as a client response
+				atomic.CompareAndSwapInt64(&claimed, -1, int64(i)) { // this checks that the qualifying response is the first response
+				serve(crw)
+				cancel()
 			}
+			return nil
 		})
 	}
 
 	// this is a fallback case for when no qualifying upstream response arrives,
 	// the first response is used, regardless of qualification
 	go func() {
-		wg.Wait()
+		eg.Wait()
 		// if claimed is still -1, the fallback case must be used
 		if atomic.CompareAndSwapInt64(&claimed, -1, -2) && r.Context().Err() == nil {
 			// this iterates the captures and serves the first non-nil response

pkg/backends/alb/mech/nlm/newest_last_modified.go

@@ -30,6 +30,7 @@ import (
 	"github.com/trickstercache/trickster/v2/pkg/proxy/headers"
 	"github.com/trickstercache/trickster/v2/pkg/proxy/request"
 	"github.com/trickstercache/trickster/v2/pkg/proxy/response/capture"
+	"golang.org/x/sync/errgroup"
 )
 
 const (
@@ -38,15 +39,18 @@ const (
 )
 
 type handler struct {
-	pool pool.Pool
+	pool    pool.Pool
+	options options.NewestLastModifiedOptions
 }
 
 func RegistryEntry() types.RegistryEntry {
 	return types.RegistryEntry{ID: ID, Name: Name, ShortName: names.MechanismNLM, New: New}
 }
 
-func New(_ *options.Options, _ rt.Lookup) (types.Mechanism, error) {
-	return &handler{}, nil
+func New(o *options.Options, _ rt.Lookup) (types.Mechanism, error) {
+	return &handler{
+		options: o.NLMOptions,
+	}, nil
 }
 
 func (h *handler) SetPool(p pool.Pool) {
@@ -94,15 +98,17 @@ func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	// Capture all responses
 	captures := make([]*capture.CaptureResponseWriter, l)
-	var wg sync.WaitGroup
-
+	var eg errgroup.Group
+	if limit := h.options.ConcurrencyOptions.GetQueryConcurrencyLimit(); limit > 0 {
+		eg.SetLimit(limit)
+	}
 	// Fanout to all healthy targets
 	for i := range l {
 		if hl[i] == nil {
 			continue
 		}
 		idx := i
-		wg.Go(func() {
+		eg.Go(func() error {
 			r2, _ := request.Clone(r)
 			r2 = request.ClearResources(r2.WithContext(ctx))
 			crw := capture.NewCaptureResponseWriter()
@@ -120,11 +126,12 @@ func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 					mu.Unlock()
 				}
 			}
+			return nil
 		})
 	}
 
 	// Wait for all responses to complete
-	wg.Wait()
+	eg.Wait()
 
 	// Write the response with the newest Last-Modified
 	if newestIdx >= 0 && newestIdx < len(captures) && captures[newestIdx] != nil {

pkg/backends/alb/mech/tsm/time_series_merge.go

@@ -17,9 +17,9 @@
 package tsm
 
 import (
+	stderrors "errors"
 	"net/http"
 	"strings"
-	"sync"
 
 	"github.com/trickstercache/trickster/v2/pkg/backends"
 	"github.com/trickstercache/trickster/v2/pkg/backends/alb/errors"
@@ -30,12 +30,14 @@ import (
 	"github.com/trickstercache/trickster/v2/pkg/backends/alb/pool"
 	"github.com/trickstercache/trickster/v2/pkg/backends/providers"
 	rt "github.com/trickstercache/trickster/v2/pkg/backends/providers/registry/types"
+	"github.com/trickstercache/trickster/v2/pkg/observability/logging"
 	"github.com/trickstercache/trickster/v2/pkg/observability/logging/logger"
 	"github.com/trickstercache/trickster/v2/pkg/proxy/handlers/trickster/failures"
 	"github.com/trickstercache/trickster/v2/pkg/proxy/headers"
 	"github.com/trickstercache/trickster/v2/pkg/proxy/request"
 	"github.com/trickstercache/trickster/v2/pkg/proxy/response/capture"
 	"github.com/trickstercache/trickster/v2/pkg/proxy/response/merge"
+	"golang.org/x/sync/errgroup"
 )
 
 const (
@@ -49,6 +51,7 @@ type handler struct {
 	mergePaths      []string        // paths handled by the alb client that are enabled for tsmerge
 	nonmergeHandler types.Mechanism // when methodology is tsmerge, this handler is for non-mergeable paths
 	outputFormat    string          // the provider output format (e.g., "prometheus")
+	tsmOptions      options.TimeSeriesMergeOptions
 }
 
 func RegistryEntry() types.RegistryEntry {
@@ -57,7 +60,10 @@ func RegistryEntry() types.RegistryEntry {
 
 func New(o *options.Options, factories rt.Lookup) (types.Mechanism, error) {
 	nmh, _ := rr.New(nil, nil)
-	out := &handler{nonmergeHandler: nmh}
+	out := &handler{
+		nonmergeHandler: nmh,
+		tsmOptions:      o.TSMOptions,
+	}
 	// this validates the merge configuration for the ALB client as it sets it up
 	// First, verify the output format is a support merge provider
 	if !providers.IsSupportedTimeSeriesMergeProvider(o.OutputFormat) {
@@ -140,25 +146,31 @@ func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	// Scatter/Gather section
 
 	accumulator := merge.NewAccumulator()
-	var wg sync.WaitGroup
-	var statusCode int
-	var statusHeader string
-	var mu sync.Mutex // protects statusCode and statusHeader
+	var eg errgroup.Group
+	if limit := h.tsmOptions.ConcurrencyOptions.GetQueryConcurrencyLimit(); limit > 0 {
+		eg.SetLimit(limit)
+	}
+
+	type result struct {
+		statusCode int
+		header     http.Header
+		mergeFunc  merge.RespondFunc
+	}
+	results := make([]result, l)
 
 	for i := range l {
 		if hl[i] == nil {
 			continue
 		}
-		wg.Go(func() {
+		eg.Go(func() error {
 			r2, _ := request.Clone(r)
 			rsc2 := &request.Resources{IsMergeMember: true, TSReqestOptions: rsc.TSReqestOptions}
 			r2 = request.SetResources(r2, rsc2)
 			crw := capture.NewCaptureResponseWriter()
 			hl[i].Handler().ServeHTTP(crw, r2)
 			rsc2 = request.GetResources(r2)
 			if rsc2 == nil {
-				logger.Warn("tsm gather failed due to nil resources", nil)
-				return
+				return stderrors.New("tsm gather failed due to nil resources")
 			}
 
 			// ensure merge functions are set on cloned request
@@ -170,27 +182,38 @@ func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 			if rsc2.MergeFunc != nil && rsc2.TS != nil {
 				rsc2.MergeFunc(accumulator, rsc2.TS, i)
 			}
-			// update status code and headers (take best status code)
-			mu.Lock()
-			if mrf == nil {
-				mrf = rsc2.MergeRespondFunc
-			}
-			if crw.StatusCode() > 0 {
-				if statusCode == 0 || crw.StatusCode() < statusCode {
-					statusCode = crw.StatusCode()
-				}
+			results[i] = result{
+				statusCode: crw.StatusCode(),
+				header:     crw.Header(),
+				mergeFunc:  rsc2.MergeRespondFunc,
 			}
-			if crw.Header() != nil {
-				headers.StripMergeHeaders(crw.Header())
-				statusHeader = headers.MergeResultHeaderVals(statusHeader,
-					crw.Header().Get(headers.NameTricksterResult))
-			}
-			mu.Unlock()
+			return nil
 		})
 	}
 
 	// wait for all fanout requests to complete
-	wg.Wait()
+	if err := eg.Wait(); err != nil {
+		logger.Warn("tsm gather failure", logging.Pairs{"error": err})
+	}
+
+	// Aggregate results sequentially - no mutex contention
+	var statusCode int
+	var statusHeader string
+	for _, res := range results {
+		if mrf == nil {
+			mrf = res.mergeFunc
+		}
+		if res.statusCode > 0 {
+			if statusCode == 0 || res.statusCode < statusCode {
+				statusCode = res.statusCode
+			}
+		}
+		if res.header != nil {
+			headers.StripMergeHeaders(res.header)
+			statusHeader = headers.MergeResultHeaderVals(statusHeader,
+				res.header.Get(headers.NameTricksterResult))
+		}
+	}
 
 	// set aggregated status header
 	if statusHeader != "" {