Upgrade test improvements for 1.20.x (#21813)

* Bump Envoy version used for 1.20.x upgrade tests

* Improve README + docstrings

.github/workflows/nightly-test-integrations-1.20.x.yml

@@ -241,7 +241,7 @@ jobs:
       # matrix.consul-version (i.e. whenever the highest common Envoy version across active
       # Consul versions changes). The minor Envoy version does not necessarily need to be
       # kept current for the purpose of these tests, but the major (1.N) version should be.
-      ENVOY_VERSION: 1.27.6
+      ENVOY_VERSION: 1.28.7
     steps:
       - name: Checkout code
         uses: actions/checkout@0ad4b8fadaa221de15dcec353f45205ec38ea70b # v4.1.4

test/integration/consul-container/test/upgrade/README.md

@@ -12,9 +12,11 @@
 
 ## Introduction
 
-The goal of upgrade tests is to ensure problem-free upgrades on supported upgrade paths. At any given time, Consul supports the latest minor release, and two older minor releases, e.g. 1.15, 1.14, and 1.13. Upgrades to any higher version are permitted, including skipping a minor version e.g. from 1.13 to 1.15.  
+The goal of upgrade tests is to ensure problem-free upgrades on supported upgrade paths.
+At any given time, Consul supports the latest minor release, and two older minor releases, e.g. 1.15, 1.14, and 1.13.
+Upgrades to any higher version are permitted, including skipping a minor version e.g. from 1.13 to 1.15.
 
-The upgrade tests also aims to highlight errors that may occur as users attempt to upgrade their current version to a newer version. 
+The upgrade tests also aim to highlight errors that may occur as users attempt to upgrade their current version to a newer version.
 
 ### How it works
 
@@ -49,7 +51,13 @@ To run the upgrade test, the following tools are required:
 
 ### Running Upgrade integration tests
 - run `make dev-docker`
-- build a consul-envoy container image `cd test/integration/consul-container docker build -t consul-envoy:latest-version --build-arg CONSUL_IMAGE=docker.mirror.hashicorp.services/consul:1.15  --build-arg ENVOY_VERSION=1.24.6  -f ./assets/Dockerfile-consul-envoy ./assets`
+- build a consul-envoy container image
+  ```shell
+  cd test/integration/consul-container
+  docker build -t consul-envoy:latest-version \
+    --build-arg CONSUL_IMAGE=docker.mirror.hashicorp.services/consul:1.20.0-rc1  \
+    --build-arg ENVOY_VERSION=1.31.2  -f ./assets/Dockerfile-consul-envoy ./assets
+  ```
 - run the single test `go test -v -timeout 30m -run ^TestACL_Upgrade_Node_Token$ ./.../upgrade/`
 - run all upgrade tests `go test -v -timeout 30m -run ./.../upgrade`
 

test/integration/consul-container/test/upgrade/peering/peering_http_test.go

@@ -95,7 +95,7 @@ func TestPeering_HTTPRouter(t *testing.T) {
 }
 
 // Verify resolver and failover can direct traffic to server in peered cluster
-// In addtional to the basic topology, this case provisions the following
+// In addition to the basic topology, this case provisions the following
 // services in the dialing cluster:
 //
 //   - a new static-client at server_0 that has two upstreams: static-server (5000)
@@ -313,6 +313,8 @@ func TestPeering_HTTPResolverAndSplitter(t *testing.T) {
 	// TODO: restart static-server-2's sidecar
 }
 
+// peeringUpgrade upgrades the accepting cluster, verifies that peering is still active,
+// and then upgrades the dialing cluster and verifies that peering is still active.
 func peeringUpgrade(t *testing.T, accepting, dialing *libtopology.BuiltCluster, targetVersion string) {
 	t.Helper()