Live with Gateway API

This is the documentation - and executable code! - for the Gateway API service mesh workshop at KubeCon NA 2024 in Salt Lake City, Utah.

The easiest way to walk through this workshop is to install demosh and execute this file with an environment variable set to select the service mesh you wish to use. Start this workshop with either Linkerd or Istio by running one of the following commands:

DEMO_MESH=linkerd demosh README.md

OR

DEMO_MESH=istio demosh README.md

---

For this workshop, you'll need a running, empty, Kubernetes cluster.

If you don't already have a cluster prepared, ensure you have the Docker daemon or compatible alternative running, k3d and kubectl installed, then run ./create-cluster.sh in a new terminal to create a local k3d cluster.

---

Configuring your service mesh with Gateway API

In this workshop, we'll be running the Faces demo application in a Kubernetes cluster, using a service mesh and an ingress controller that we'll configure using the Gateway API. Our choices here are

• Linkerd with Envoy Gateway, or
• Istio (with Istio ingress gateway)

We'll start by installing the service mesh and the Gateway API CRDs and do any additional setup the ingress controller needs. Next we'll create the namespace for our Faces demo app and set it up for mesh injection. Finally, we'll install the Faces demo application and get going!

First, we'll confirm that we're using the Kubernetes cluster we expect.

kubectl cluster-info

OK, so far so good!

Installing the Gateway API CRDs

Gateway API is a CRD API: we need the CRDs to be present to use Gateway API. Additionally, we need to choose between the experimental channel and the standard channel: for this workshop, we'll use the experimental channel of Gateway API v1.1.1. (At the moment, Linkerd can't use the v1.2.0 experimental channel, because it doesn't have GRPCRoute v1alpha2 any more.)

So let's get v1.1.1 experimental installed first. This repo contains the YAML for that already, pre-downloaded from

https://github.com/kubernetes-sigs/gateway-api/releases/\
    download/v1.1.1/experimental-install.yaml

so we can just apply it:

kubectl apply -f gateway-api/experimental-install.yaml

Getting the Mesh Installed

Once we have the CRDs, let's get our service mesh installed!

#@immed
$SHELL ${DEMO_MESH}/install.md

Creating the Gateway

OK, the mesh is running now, so let's install our GatewayClass and Gateway.

#@immed
$SHELL ${DEMO_MESH}/create-gateway.md
#@immed
INGRESS_IP=$(bash ${DEMO_MESH}/get-ingress-ip.sh)
#@immed
echo "Ingress is running at $INGRESS_IP"

Installing Faces

OK! It's time to install the Faces demo application. We'll start by setting up the namespace that Faces will use: first we create it...

kubectl create namespace faces

...and then we'll set it up for mesh enrollment.

#@immed
$SHELL ${DEMO_MESH}/setup-namespace.md

Next up, we use Helm to install the Faces application. The Faces application works by installing a face workload which calls the smiley and color workloads. smiley returns a grinning face; color returns the color blue; face combines these and returns the combination to the GUI.

Faces is usually set up so that it fails a lot, but since this workshop is about Gateway API, we'll turn that off (mostly), and we'll also install three versions each of smiley and color so we can route between them later on. All of that is in our faces/values.yaml file; it's not very interesting to look at so we won't show it here.

helm install faces \
     -n faces \
     oci://ghcr.io/buoyantio/faces-chart \
     --version 2.0.0-rc.1 \
     --values faces/values.yaml

After that, wait for the Faces application to be ready...

kubectl rollout status -n faces deploy

...and then we should be able to go to Faces GUI in the web browser, at http://${INGRESS_IP}/gui/ (or http://localhost/gui/ for some local cluster setups), and see good things (hopefully)!

The Ingress Problem

OK, well, that didn't work. The reason is that we haven't actually told our Gateway controller how to direct traffic to the GUI. We need to create an HTTPRoute to do that - specifically, any HTTP request with a path starting with /gui should go to the faces-gui service. This gives your web browser a way to download the GUI code itself.

bat k8s/01-base/gui-route.yaml
kubectl apply -f k8s/01-base/gui-route.yaml

If we try the web browser again, we should now get the GUI! But we'll see all grimacing faces on purple backgrounds. This is because the GUI, for each cell, tries to request the /face/ path, which we haven't added a route for yet.

To tackle that, we'll create another HTTPRoute to direct any request with a path starting with /face to the face service.

bat k8s/01-base/face-route.yaml
kubectl apply -f k8s/01-base/face-route.yaml

And now, finally, our web browser should show us all grinning faces on blue backgrounds, because we've used Gateway API to tell our Gateway controller how to route traffic from outside the mesh to the Faces application!

Mesh Routing with HTTP

Next up: what can Gateway API do in the mesh?

The simplest next step is the moral equivalent of the HTTPRoutes we just installed to allow ingress: unconditionally route traffic within the mesh.

With ingress traffic, we used a parentRef to attach our HTTPRoute to the Gateway we created. For mesh traffic, we'll use a parentRef that points to a Service to intercept traffic to that Service. For example, here's the simplest HTTPRoute we can create for traffic to the smiley service:

bat k8s/02-unconditional/smiley-simplest.yaml

We're not going to bother applying this route because it doesn't do anything: since it has no backendRefs, it'll just route traffic directed to the smiley service to... the smiley service. But if we add a backendRef, we can send the traffic somewhere else. For example, we could send all traffic meant for the smiley Service to smiley2 instead:

bat k8s/02-unconditional/smiley-route.yaml

The smiley2 workload returns a heart-eyed smiley instead of a grinning smiley, so when we apply that route, we'll immediately see all the cells change to heart-eyed smilies.

kubectl apply -f k8s/02-unconditional/smiley-route.yaml

Mesh Routing with gRPC

We can do exactly the same for gRPC, too. In the Faces demo, the face workload uses HTTP to call smiley, but gRPC to call color. We can route all the color traffic over to color2 using a simple GRPCRoute:

bat k8s/02-unconditional/color-route.yaml

color returns blue, but color2 returns green, so when we apply this route, we'll see all the cells change to green.

kubectl apply -f k8s/02-unconditional/color-route.yaml

Operational Concerns

In practice, this kind of unconditional routing is usually not a great idea. For one thing, its all-at-once nature is dangerous: suppose we sent all the smiley traffic over to smiley2 only to find that smiley2 was broken? The only good thing about that situation is that we'd be able to shift back to smiley just as quickly.

(That's assuming that we noticed that smiley2 was broken right away, of course. If we didn't, we'd have a lot of unhappy users before we figured out what was going on. Worst case, we would already have shut down smiley, and recovery would be that much harder.)

Canaries

In the real world, a much smarter move is to randomly assign only a little bit of incoming traffic to a new workload. If things go well, we can gradually do more and more traffic until it's all shifted over. This is the canary deployment, which is the basis of progressive delivery.

To demonstrate this with Gateway API, we'll first reset Faces by deleting our unconditional routes:

kubectl delete -n faces httproute smiley-route
kubectl delete -n faces grpcroute color-route

We'll see all the cells go back to grinning smilies and blue backgrounds, and we can then start our canary demonstration by sending just 10% of the traffic meant for smiley to smiley2:

bat k8s/03-canary/smiley-canary-10.yaml

When we apply this, we'll start to see just a few heart-eyed smilies.

kubectl apply -f k8s/03-canary/smiley-canary-10.yaml

We can change the fraction of traffic being diverted in realtime, simply by changing the weights in the HTTPRoute:

diff -u99 --color=always k8s/03-canary/smiley-canary-{10,50}.yaml
kubectl apply -f k8s/03-canary/smiley-canary-50.yaml

Once we're happy that all is well, that's when we switch all the traffic over to smiley2:

diff -u99 --color=always k8s/03-canary/smiley-canary-{50,100}.yaml
kubectl apply -f k8s/03-canary/smiley-canary-100.yaml

To prove that the smiley workload isn't doing anything, we can scale it down to zero with no effect on what we see.

kubectl scale -n faces deploy/smiley --replicas=0

Operational Concerns

It's worth calling out that we're now in a state that is not a good idea, operationally speaking. To see why, imagine that it's six weeks later, something is going wrong with smilies, and the on-call engineer is someone who wasn't at this workshop.

They've been told that the first place to start is the face workload's logs, so they go there:

kubectl logs -n faces deploy/face -c face | head

"Great!" they think. "face must be getting smilies from http://smiley, so I can go look at the smiley workload to see what's up!"

This is where things start to go wrong. We who were at this workshop know that there's an HTTPRoute redirecting all the smiley traffic to smiley2, but our on-call engineer doesn't know that. They'll get very confused when they realize that there aren't even any smiley pods to look at.

Hopefully they'll have been trained about Gateway API, of course! so hopefully they'll know to look for routes. But the right way to deal with this, operationally, is to deploy a smiley workload that returns heart-eyed smilies, then remove the nonintuitive routing. That way, anyone looking to see what's going on won't need to find the HTTPRoute in order to make sense of everything.

Operational Concerns

For this workshop, though, we're not going to do that -- we'll just reset the world again by scaling smiley back up with grinning smilies and deleting our HTTPRoute:

kubectl scale -n faces deploy/smiley --replicas=1
kubectl rollout status -n faces deploy
kubectl delete -n faces httproute smiley-canary

At this point, we're back to grinning smilies, and we're getting them from the smiley workload as we'd expect.

Canaries with gRPC

We can canary gRPC services, too! The Faces demo uses gRPC for the color workload, and we can canary between color (blue) and color2 (green) just as easily as we did for our smilies:

bat k8s/03-canary/color-canary-25.yaml
kubectl apply -f k8s/03-canary/color-canary-25.yaml

We'll now see some green cells in the GUI, but still mostly blue. Of course, we can adjust the weights on the fly just like we did with the HTTPRoute:

diff -u99 --color=always k8s/03-canary/color-canary-{25,50}.yaml
kubectl apply -f k8s/03-canary/color-canary-50.yaml

At this point we'll have a 50/50 split between blue and green cells. Let's leave it there for the moment while we see what else we can do.

Dynamic Routing

Gateway API also allows us to make routing decisions based on various information in the request itself, like the path, headers, or query parameters. In our previous example, we did a canary based on the Service to which the request was sent, but Faces also provides a different Path depending on whether it's making a request for an edge cell or a center cell.

Let's send all the edge cells to smiley2, with its heart-eyed smilies. This should leave the center cells still calling smiley, so they should still show us grinning smilies.

bat k8s/03-canary/smiley-edge.yaml
kubectl apply -f k8s/03-canary/smiley-edge.yaml

There we go: all the edge cells are showing us heart-eyed smilies, while the center cells are still grinning smilies.

Dynamic Canarying

We can combine this with a canary, of course. Here we'll send 50% of the edge traffic to smiley3, which returns rolling-eyes smilies, leaving the other half going to smiley2 (heart-eyed smilies).

bat k8s/03-canary/smiley-edge-canary-50.yaml
kubectl apply -f k8s/03-canary/smiley-edge-canary-50.yaml

Rollback

smiley3 seems to have a problem -- half the time it's not returning a face with rolling eyes at all! Instead, it's returning the cursing face, which is not what it should do. So let's roll back to the previous state -- nothing requires that you always take a canary to completion.

To roll back, we'll just reapply the previous HTTPRoute, so that we still get heart-eyed smileys for the edge cells.

bat k8s/03-canary/smiley-edge.yaml
kubectl apply -f k8s/03-canary/smiley-edge.yaml

Now we're right back to the way things were, and we can fix the problem at our leisure without the stress of having our production traffic broken while we work on a fix.

And, of course, we could be even more drastic and just delete the HTTPRoute entirely. In this case, that will return the world back to all grinning smilies.

kubectl delete -n faces httproute smiley-edge

Dynamic Routing with gRPC

We can also do dynamic routing with gRPC services. Where the smiley workload uses two separate paths, the color workload provides two separate gRPC methods: the Center method and the Edge method. We can route these to different workloads, just as we did with the smiley service -- here we'll send all the edge cells to color2, which returns green.

bat k8s/03-canary/color-edge.yaml
kubectl apply -f k8s/03-canary/color-edge.yaml

Now we have all green cells at the edge -- but wait. We're still seeing some green in the center cells. Any guesses as to why?

Conflict Resolution

The reason is that we still have the color-canary GRPCRoute in place. In Gateway API in general, more specific routes win over less specific routes, so while the color-edge GRPCRoute wins whenever the Edge method is in play, when it's not in play the color-canary GRPCRoute still applies!

If we delete color-canary, we'll see all blue in the center and all green at the edge.

kubectl delete -n faces grpcroute color-canary

Immediate Effect

Note that, in every case, changing the Gateway API resources has an immediate effect on what's going on in the application: we don't have to restart things, or wait for a new pod to come up, or anything like that. This kind of control is one of the huge advantages of this kind of self-service model.

Additionally, everything we've been doing with HTTPRoutes and GRPCRoutes is the kind of thing that should be accessible to the application developer, without needing to know anything about the underlying infrastructure. This is the win of persona-based API design: if you do it correctly, the things that each persona needs to do are easily accessible to them.

A/B Testing

Another common use case for Gateway API is A/B testing: sending just part of your traffic to a new destination, based on a header or some other attribute of the request. The classic example here is to base the decision on which user is logged in, so that's what we'll do... if "logged in" isn't too strong a term for a demo that lets you pick who you're logged in as with no authentication at all!

Under the hood, when you enter a username in the Faces GUI, it sets the X-Faces-User header in the requests being sent. This header gets propagated everywhere in the app, so we can use it for A/B testing. Let's start by doing an A/B test for the smiley service: we'll arrange for the heart user to get heart-eyed smilies, and everyone else to get grinning smilies.

bat k8s/04-abtest/smiley-ab.yaml
kubectl apply -f k8s/04-abtest/smiley-ab.yaml

The Faces GUI allows us to switch the user we're "logged in" as by editing the username above the cell grid. We can best see the effect of the A/B test by using two browsers for this, one logged in as heart and one logged in as anything else (or not logged in at all). Since the GUI sends the logged-in username as the value of the X-Faces-User header, the heart browser should see heart-eyed smilies, but the other should see grinning smilies.

If we do this, and find that everyone really loves heart-eyed smilies, we can make sure of that by unconditionally routing all the traffic to smiley2:

bat k8s/04-abtest/smiley2-unconditional.yaml
kubectl apply -f k8s/04-abtest/smiley2-unconditional.yaml

Normally, as noted before, you'd clean up the Deployments after this. For the moment, though, we'll just delete the HTTPRoute (which will switch everyone back to grinning smilies).

kubectl delete -n faces httproute smiley-a-b

A/B Testing

We can do the same trick with gRPC, too. Let's give all the heart users the dark-blue color from color3:

bat k8s/04-abtest/color-ab.yaml
kubectl apply -f k8s/04-abtest/color-ab.yaml

Now we have dark blue cells at the center -- but we're still seeing green at the edges? Why is that?

Conflict Resolution

This is another aspect of the conflict resolution rules. We currently have two GRPCRoutes in play:

kubectl get -n faces grpcroute

color-a-b is doing our A/B test: it specifies matches on the gRPC Service and a header. color-edge is doing our edge/cell routing: it specifies matches on the gRPC Service and the gRPC method. These are basically equivalent in terms of specificity, so the older route wins -- and for the edge cells where color-edge matches, color-edge is older than color-a-b.

Deleting color-edge will let us see all dark blue cells.

kubectl delete -n faces grpcroute color-edge

The conflict resolution rules are a critical part of Gateway API, but they're not always intuitive -- once multiple rules are in play, testing is very important.

A/B Testing

Back to our A/B test, there's nothing preventing us from doing an A/B test of smiley at the same time as color:

kubectl apply -f k8s/04-abtest/smiley-ab.yaml

In the real world, running multiple A/B tests simultaneously like this can be a bit of a mess, but the tooling supports it if you want to!

For now, let's go ahead and shut the A/B tests down by deleting the routes:

kubectl delete -n faces httproute smiley-a-b
kubectl delete -n faces grpcroute color-a-b

Once again, we'll be back to grinning faces on blue backgrounds.

Timeouts

OK, we've done canaries and A/B testing. Now let's look at timeouts. Every cell fading away is a request that's taking too long -- we'll add some timeouts to improve that, starting from the bottom of the call graph.

Note that timeouts are not about protecting the service: they are about providing agency to the client by giving the client a chance to decide what to do when things take too long. They actually increase load on the workload.

Unfortunately, for now, we have to do timeouts slightly differently in the different meshes. Linkerd currently uses its own policy.linkerd.io HTTPRoute for timeout support. Istio, on the other hand, uses the timeouts field in the official Gateway API HTTPRoute.

We'll start by adding a timeout to the smiley Service. If the face workload's request to smiley times out, the GUI will show this as a sleeping face.

bat k8s/05-timeouts/smiley-timeout-${DEMO_MESH}.yaml
kubectl apply -f k8s/05-timeouts/smiley-timeout-${DEMO_MESH}.yaml

Timeouts

Finally, we'll add a timeout for the GUI's calls to face itself. We'll do this a bit differently: when the GUI sees a timeout talking to the face service, it will just keep showing the user the old data for awhile. There are a lot of applications where this makes an enormous amount of sense: if you can't get updated data, the most recent data may still be valuable for some time! Eventually, though, the app should really show the user that something is wrong: in our GUI, repeated timeouts eventually lead to a faded sleeping-face cell with a pink background.

For the moment, too, the GUI will show a counter of timed-out attempts, to make it a little more clear what's going on.

We'll use our Gateway controller to implement this timeout, rather than the mesh, illustrating that there can be a lot of overlap between these two components. Also note that we already have an HTTPRoute for the /face/ path, so we'll add the timeout to that route, rather than creating a new one.

diff -u99 --color=always k8s/{01-base,05-timeouts}/face-route.yaml
kubectl apply -f k8s/05-timeouts/face-route.yaml

We should now start seeing counters appear -- and after long enough, we should see faded cells.

What About the Color Workload?

We can't actually demonstrate a timeout on the color workload, because Gateway API doesn't yet include GRPCRoute timeouts...

...but cross your fingers for them at KubeCon in London!

Wrapping Up

So that's the Gateway API, with HTTP and gRPC canaries, A/B testing, and timeouts, managing a Gateway controller and a service mesh!

If you have any questions or feedback, please feel free to reach out to us on Kubernetes Slack, or via email to [email protected] or [email protected]. Gateway API is evolving, too, so keep an eye out for more at KubeCon in London!