fix: reject fetch when the client SSE stream is on another replica

deploy/helm/kubeview/values.yaml

@@ -71,6 +71,9 @@ podSecurityContext: {}
 securityContext: {}
 
 # -- Run multiple instances of the Kubeview pod
+# NOTE: With more than one replica, clients need sticky sessions (session affinity) on the
+# Service or ingress, so a browser's SSE event stream and its API calls reach the same pod.
+# Without them live updates will not work, see https://github.com/benc-uk/kubeview/issues/185
 replicaCount: 1
 
 # -- This is for changing the resource limits and requests for the Kubeview pods

frontend/js/main.js

@@ -289,18 +289,30 @@ Alpine.data('mainApp', () => ({
 
     let data
     let res
-    try {
-      res = await fetch(`api/fetch/${this.namespace}?clientID=${getClientId()}`)
-      if (!res.ok) throw new Error(`HTTP error ${res.status}: ${res.statusText}`)
-      data = await res.json()
-
-      this.isLoading = false
-      this.showWelcome = false
-    } catch (err) {
-      this.showError(`Failed to fetch namespace data: ${err.message}`, res)
-      return
+    const maxAttempts = 5
+    for (let attempt = 1; ; attempt++) {
+      try {
+        res = await fetch(`api/fetch/${this.namespace}?clientID=${getClientId()}`)
+        // 409 means the client's SSE stream is connected to a different pod, which can happen
+        // with multiple replicas and no sticky sessions. Retrying should eventually land the
+        // fetch on the same pod as the SSE stream. See https://github.com/benc-uk/kubeview/issues/185
+        if (res.status === 409 && attempt < maxAttempts) {
+          console.warn(`⚠️ SSE stream not on this pod, retrying fetch (${attempt}/${maxAttempts})`)
+          await new Promise((resolve) => setTimeout(resolve, 250))
+          continue
+        }
+        if (!res.ok) throw new Error(`HTTP error ${res.status}: ${res.statusText}`)
+        data = await res.json()
+        break
+      } catch (err) {
+        this.showError(`Failed to fetch namespace data: ${err.message}`, res)
+        return
+      }
     }
 
+    this.isLoading = false
+    this.showWelcome = false
+
     if (this.cfg.debug) {
       console.log('📦 Fetched data:', data)
     }

go.mod

@@ -67,3 +67,5 @@ require (
 	sigs.k8s.io/structured-merge-diff/v6 v6.4.2 // indirect
 	sigs.k8s.io/yaml v1.6.0 // indirect
 )
+
+replace github.com/benc-uk/go-rest-api => github.com/davidgrldo/go-rest-api v1.1.1-fix.185

go.sum

@@ -1,5 +1,3 @@
-github.com/benc-uk/go-rest-api v1.1.0 h1:bLyUPPl/R52cpjzu8EavQxnNtUlaXt0ad5WmBiMjOUk=
-github.com/benc-uk/go-rest-api v1.1.0/go.mod h1:l6SGcra0vweKQ7XHC7vooGnMAr8QjRdeP+gVwUObX24=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
 github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
 github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
@@ -8,6 +6,8 @@ github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSs
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc h1:U9qPSI2PIWSS1VwoXQT9A3Wy9MM3WgvqSxFWenqJduM=
 github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davidgrldo/go-rest-api v1.1.1-fix.185 h1:tMrHp7uGpEZZwR21tZXjUMHo61OnDw13vDel42kXQVw=
+github.com/davidgrldo/go-rest-api v1.1.1-fix.185/go.mod h1:l6SGcra0vweKQ7XHC7vooGnMAr8QjRdeP+gVwUObX24=
 github.com/elastic/go-sysinfo v1.15.5 h1:fCVUDmjHgljLUQCygherMnsRRJ9AkuAQIywTL7dEH28=
 github.com/elastic/go-sysinfo v1.15.5/go.mod h1:ZBVXmqS368dOn/jvijV/zHLfakWTYHBZPk3G244lHrU=
 github.com/elastic/go-windows v1.0.2 h1:yoLLsAsV5cfg9FLhZ9EXZ2n2sQFKeDYrHenkcivY4vI=

server/routes.go

@@ -10,6 +10,7 @@ import (
 	"log"
 	"net/http"
 	"regexp"
+	"slices"
 	"strconv"
 
 	"github.com/benc-uk/go-rest-api/pkg/problem"
@@ -139,6 +140,20 @@ func (s *KubeviewAPI) handleFetchData(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Guard: with multiple replicas and no sticky sessions, the browser's SSE
+	// stream may be connected to a different pod than this request landed on.
+	// Joining the group here would create a group member with no SSE channel on
+	// this pod, so the client would never receive any events. Reject the
+	// request instead, so the frontend can retry and land on the right pod.
+	// See https://github.com/benc-uk/kubeview/issues/185
+	if !slices.Contains(s.eventBroker.GetClients(), clientID) {
+		log.Printf("⚡ Client %s has no SSE connection on this pod, rejecting fetch", strconv.Quote(clientID))
+		problem.Wrap(409, r.RequestURI, "client not connected",
+			errors.New("clientID has no SSE connection to this pod, retry the request")).Send(w)
+
+		return
+	}
+
 	// Critical: Puts the client in the correct SSE group for this namespace
 	// Events are sent to this group, so the client will receive updates ONLY for this namespace
 	s.eventBroker.RemoveFromAllGroups(clientID)