Part 3: Deploying Envoy as an API Gateway for Microservices

Flynn   /    May 9, 2017

An API Gateway is a façade that sits between the consumers and producers of an API. Cross-cutting functionality such as authentication, monitoring, and traffic management is implemented in your API Gateway so that your services can remain unaware of these details. In addition, when multiple services are responsible for different APIs (e.g., in a microservices architecture), an API Gateway hides this abstraction detail from the consumer.

There are dozens of different options for API Gateways, depending on your requirements. The Amazon API Gateway is a hosted Gateway that runs in Amazon. Kong is a popular open source API gateway. Or you could build your own on top of a Layer 7 proxy such as Traefik, NGINX, HAProxy, or Envoy. These all have their various strengths and weaknesses.

In general, though, you want to pick an API gateway that can accelerate your development workflow. Traditional API gateways focus on the challenges of API management, so using an API gateway that enables rapid development of services is essential.

Here at Datawire, we've been using Envoy for microservices. Envoy is interesting because, in addition to providing the reverse proxy semantics you need to implement an API Gateway, it also supports the features you need for distributed architectures (in fact, the Istio project builds on Envoy to provide a full-blown services mesh).

So let's take a closer look at deploying Envoy as a full-fledged, self-service API gateway. If you've been following along with our Envoy tutorial so far, we've done the following:

  1. Create a Docker container based on the official Docker image
  2. Crafted an Envoy configuration file
  3. Deployed Envoy with the appropriate configuration file

Introducing Ambassador

This approach starts to get cumbersome as you add complexity to your deployment. For example, every configuration change requires editing a (complex!) configuration file, and redeploying Envoy. And, we've glossed over the operational aspects of keeping multiple Envoy instances running for scalability and availability.

We thought there would be an easier way, so we wrote Ambassador. Here's what Ambassador does:

  • Makes it easy to change and add to your Envoy configuration via Kubernetes annotations
  • Adds the out-of-the-box configuration necessary for production Envoy, e.g., monitoring, health/liveness checks, and more
  • Extends Envoy with traditional API Gateway functionality such as authentication
  • Integrates with Istio, for organizations who need a full-blown service mesh

Ambassador only deploys in Kubernetes. This means that Ambassador delegates all the hard parts of scaling and availability to Kubernetes. Want to upgrade Ambassador with no downtime? No problem -- just use a Kubernetes rolling update.

Setting Up

We're going to assume that your basic infrastructure is set up enough that you have a Kubernetes cluster running in your cloud environment of choice. For now, we assume that:

  • You have kubectl correctly talking to a Kubernetes cluster running in EC2 or GKE.
    • This is probably obvious, but it's tough to work with a Kubernetes cluster if you can't talk to it with kubectl.
  • You have docker installed and working.
    • Since we'll be building Docker images, we need a working docker command.
  • You have credentials to push Docker images to either Docker Hub or the Google Container Registry (gcr.io).

That last point is worth a little more discussion. To run something in Kubernetes, we have to be able to pull an Docker image from somewhere that the cluster can reach. When using Minikube, this is no problem, since Minikube runs its own Docker daemon: by definition, anything in the Minikube cluster can talk to that Docker daemon. However, things are different once GKE or EC2 come into play: they can't talk to a Docker daemon on your laptop without heroic measures, so you'll need to explicitly push images somewhere accessible.

The Ambassador service

Ambassador is deployed as a Kubernetes service. The following configuration will create a service for Ambassador. It also adds a mapping that will route traffic from /httpbin/ to the public httpbin.org service.

---
apiVersion: v1
kind: Service
metadata:
  labels:
    service: ambassador
  name: ambassador
  annotations:
    getambassador.io/config: |
      ---
      apiVersion: ambassador/v0
      kind:  Mapping
      name:  httpbin_mapping
      prefix: /httpbin/
      service: httpbin.org:80
      host_rewrite: httpbin.org
spec:
  type: LoadBalancer
  ports:
  - name: ambassador
    port: 80
    targetPort: 80
  selector:
    service: ambassador

By using Kubernetes annotations, Ambassador integrates transparently into your existing Kubernetes deployment workflow, so tools such as Forge or Kubernetes deploy work naturally with Ambassador.

Save the above YAML into a file called ambassador-service.yaml, and type kubectl apply -f ambassador-service.yaml to deploy the service.

Starting Ambassador

We have an Ambassador service, but we don't actually have Ambassador running. To do this, we'll need a Kubernetes deployment. If you're using a cluster with RBAC enabled, you'll need to use:

kubectl apply -f https://getambassador.io/yaml/ambassador/ambassador-rbac.yaml

Without RBAC, you can use:

kubectl apply -f https://getambassador.io/yaml/ambassador/ambassador-no-rbac.yaml

Once that's done, you should see three pods for Ambassador:

$ kubectl get pods
NAME                                READY     STATUS    RESTARTS   AGE
ambassador-1378270275-51qns         2/2       Running   0          2m
ambassador-1378270275-kr361         2/2       Running   0          2m
ambassador-1378270275-v10x8         2/2       Running   0          2m

$ kubectl get services
NAME               CLUSTER-IP        EXTERNAL-IP        PORT(S)    AGE
ambassador         109.168.235.177   a1128c0831f9e...   80/TCP     3m
kubernetes         109.164.0.1       <none>             443/TCP    9m

Ambassador relies on Kubernetes for replication, availability, and scaling -- making Ambassador itself very simple. Ambassador also relies on Kubernetes for persistence, so Ambassador has no database.

Setting AMBASSADORURL

In order to get access to your microservices through Ambassador, you'll need an external URL to Ambassador's service interface. We'll use $AMBASSADORURL as shorthand for the base URL of Ambassador.

We'll need to start by getting the external IP address of Ambassador. You can get the IP address by running kubectl describe service ambassador and looking at the LoadBalancer Ingress line. (On Minikube, you'll need to use minikube service --url ambassador.) Set the value of AMBASSADORURL to this address, e.g.,:

export AMBASSADORURL=109.34.24.5

In any case, do not include a trailing / in $AMBASSADORURL, or the examples in this document won't work.

Testing Ambassador

We can now speak to the httpbin service using Ambassador:

$ curl $AMBASSADORURL/httpbin/ip/

This will send a request to Ambassador, which then routes the request to the httpbin service.

Diagnostics

Under the hood, Ambassador relies on Envoy (and its powerful feature set) for routing, TLS, and the like. Ambassador includes diagnostics that gives more insight into the Envoy configuration that Ambassador is managing. These diagnostics are not publicly exposed by default.

You can access the diagnostics by getting the list of Ambassador pods:

$ kubectl get pods
NAME                                READY     STATUS    RESTARTS   AGE
ambassador-1378270275-51qns         2/2       Running   0          2m
ambassador-1378270275-kr361         2/2       Running   0          2m
ambassador-1378270275-v10x8         2/2       Running   0          2m

forwarding to port 8877 on one of the pods:

kubectl port-forward ambassador-1378270275-51qns 8877

And then visiting http://localhost:8877 in your web browser.

Up Next

In this article, we've shown how you can deploy Envoy as an API Gateway using Ambassador. Envoy has many powerful features such as sophisticated load balancing algorithms, advanced statistics monitoring, and more. Ambassador exposes many of these features through annotations to support use cases. To learn more, read about Canary deployments or see how to use Prometheus to monitor Envoy and Ambassador.

Questions?

We’re happy to help! Look for answers in the rest of the Microservices Architecture Guide, join our Gitter chat, send us an email at hello@datawire.io, or contact our sales team.