[8.16](backport #3991) Don't fail checkin if agent has upgrade details with no action

changelog/fragments/1728652985-Dont-fail-checkin-if-upgrade-action-not-found.yaml

@@ -0,0 +1,35 @@
+# Kind can be one of:
+# - breaking-change: a change to previously-documented behavior
+# - deprecation: functionality that is being removed in a later release
+# - bug-fix: fixes a problem in a previous version
+# - enhancement: extends functionality but does not break or fix existing behavior
+# - feature: new functionality
+# - known-issue: problems that we are aware of in a given version
+# - security: impacts on the security of a product or a user’s deployment.
+# - upgrade: important information for someone upgrading from a prior version
+# - other: does not fit into any of the other categories
+kind: feature
+
+# Change summary; a 80ish characters long description of the change.
+summary: Dont fail checkin if upgrade action not found
+
+# Long description; in case the summary is not enough to describe the change
+# this field accommodate a description without length limits.
+# NOTE: This field will be rendered only for breaking-change and known-issue kinds at the moment.
+description:
+  On agent checkin, when an agent has upgrade details, the corresponding agent action is looked up and linked with APM spans.
+  However, there may be cases where such an action does not exist, e.g. when running `elastic-agent upgrade` for a Fleet-managed agent.
+  This change ensures that agent checkin does not fail if the agent has upgrade details but no corresponding action.
+
+# Affected component; usually one of "elastic-agent", "fleet-server", "filebeat", "metricbeat", "auditbeat", "all", etc.
+component:
+
+# PR URL; optional; the PR number that added the changeset.
+# If not present is automatically filled by the tooling finding the PR where this changelog fragment has been added.
+# NOTE: the tooling supports backports, so it's able to fill the original PR number instead of the backport PR number.
+# Please provide it if you are adding a fragment for a different PR.
+pr: https://github.com/elastic/fleet-server/pull/3991
+
+# Issue URL; optional; the GitHub issue related to this changeset (either closes or is part of).
+# If not present is automatically filled by the tooling with the issue linked to the PR number.
+#issue: https://github.com/owner/repo/1234

internal/pkg/api/handleCheckin.go

@@ -415,7 +415,8 @@ func (ct *CheckinT) processUpgradeDetails(ctx context.Context, agent *model.Agen
 		}
 		if len(actions) == 0 {
 			vSpan.End()
-			return fmt.Errorf("upgrade_details no action for id %q found", details.ActionId)
+			zerolog.Ctx(vCtx).Warn().Msgf("upgrade_details no action for id %q found (agent id %q)", details.ActionId, agent.Agent.ID)
+			return nil
 		}
 		action = actions[0]
 		ct.cache.SetAction(action)

testing/e2e/api_version/client_api_current.go

@@ -350,6 +350,29 @@ func (tester *ClientAPITester) TestCheckinWithBadRequest() {
 	tester.Require().Equal(http.StatusBadRequest, statusCode, "Expected status code 400 for bad request")
 }
 
+func (tester *ClientAPITester) TestCheckinWithActionNotFound() {
+	ctx, cancel := context.WithTimeout(context.Background(), 4*time.Minute)
+	defer cancel()
+
+	// enroll agent
+	tester.T().Log("test enrollment")
+	agentID, agentKey := tester.Enroll(ctx, tester.enrollmentKey)
+	tester.VerifyAgentInKibana(ctx, agentID)
+
+	tester.T().Logf("test checkin with no upgrade action: agent %s", agentID)
+	// checkin request with upgrade details
+	req := &api.AgentCheckinJSONRequestBody{
+		Status:  api.CheckinRequestStatusOnline,
+		Message: "test checkin",
+		UpgradeDetails: &api.UpgradeDetails{
+			ActionId: "test-missing-id",
+			State:    api.UpgradeDetailsStateUPGDOWNLOADING,
+		},
+	}
+	_, _, statusCode := tester.Checkin(ctx, agentKey, agentID, nil, nil, req)
+	tester.Require().Equal(http.StatusOK, statusCode, "Expected status code 200 for successful checkin with action not found")
+}
+
 func (tester *ClientAPITester) TestFullFileUpload() {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()