gRPC Connections

Ambassador Edge Stack makes it easy to access your services from outside your application. This includes gRPC services, although a little bit of additional configuration is required: by default, Envoy connects to upstream services using HTTP/1.x and then upgrades to HTTP/2 whenever possible. However, gRPC is built on HTTP/2 and most gRPC servers do not speak HTTP/1.x at all. Ambassador Edge Stack must tell its underlying Envoy that your gRPC service only wants to speak to that HTTP/2, using the grpc attribute of a Mapping.

Writing a gRPC service for Ambassador Edge Stack

There are many examples and walkthroughs on how to write gRPC applications so that is not what this article will aim to accomplish. If you do not yet have a service written you can find examples of gRPC services in all supported languages here: gRPC Quickstart

This document will use the gRPC python helloworld example to demonstrate how to configure a gRPC service with Ambassador Edge Stack.

Follow the example up through Run a gRPC application to get started.

Dockerize

After building our gRPC application and testing it locally, we need to package it as a Docker container and deploy it to Kubernetes.

To run a gRPC application, we need to include the client/server and the protocol buffer definitions.

For gRPC with python, we need to install grpcio and the common protos.

Create the container and test it:

Where <docker_reg> is your Docker user or registry.

Switch to another terminal and from the same directory, run the greeter_client. The output should be the same as running it outside of the container.

Once you verify the container works, push it to your Docker registry:

Mapping gRPC services

Ambassador Edge Stack Mappings are based on URL prefixes; for gRPC, the URL prefix is the full-service name, including the package path (package.service). These are defined in the .proto definition file. In the example proto definition file we see:

so the URL prefix is helloworld.Greeter and the mapping would be:

Note the grpc: true line - this is what tells Envoy to use HTTP/2 so the request can communicate with your backend service. Also note that you'll need prefix and rewrite the same here, since the gRPC service needs the package and service to be in the request to do the right thing.

Deploying to Kubernetes

grpc_example.yaml

The Host is declared here because we are using gRPC without TLS. Since Ambassador Edge Stack terminates TLS by default, in the Host we add a requestPolicy which allows insecure connections. After adding the Ambassador Edge Stack mapping to the service, the rest of the Kubernetes deployment YAML file is pretty straightforward. We need to identify the container image to use, expose the containerPort to listen on the same port the Docker container is listening on, and map the service port (80) to the container port (50051).

For more information on insecure routing, please refer to the Host documentation.

Once you have the YAML file and the correct Docker registry, deploy it to your cluster with kubectl.

Testing the Deployment

Make sure to test your Kubernetes deployment before making more advanced changes (like adding TLS). To test any service with Ambassador Edge Stack, we will need the hostname of the running Ambassador Edge Stack service which you can get with:

Which should return something similar to:

where EXTERNAL-IP is the $AMBASSADORHOST and 80 is the $PORT.

You will need to open the greeter_client.py and change localhost:50051 to $AMBASSADORHOST:$PORT

After making that change, simply run the client again and you will see the gRPC service in your cluster respond:

gRPC and TLS

There is some extra configuration required to connect to a gRPC service through Ambassador Edge Stack over an encrypted channel. Currently, the gRPC call is being sent over cleartext to Ambassador Edge Stack which proxies it to the gRPC application.

If you want to add TLS encryption to your gRPC calls, first you need to tell Ambassador Edge Stack to add ALPN protocols which are required by HTTP/2 to do TLS.

For example:

Next, you need to change the client code slightly and tell it to open a secure RPC channel with Ambassador Edge Stack.

grpc.ssl_channel_credentials(root_certificates=None, private_key=None, certificate_chain=None)returns the root certificate that will be used to validate the certificate and public key sent by Ambassador Edge Stack. The default values of None tells the gRPC runtime to grab the root certificate from the default location packaged with gRPC and ignore the private key and certificate chain fields. Generally, passing no arguments to the method that requests credentials gives the same behavior. Refer to the languages API Reference if this is not the case.

Ambassador Edge Stack is now terminating TLS from the gRPC client and proxying the call to the application over cleartext.

If you want to configure authentication in another language, gRPC provides examples with proper syntax for other languages.

Working with Host headers that include the port

Some gRPC clients automatically include the port in the Host header. This is a problem when using TLS because the certificate will match myurl.com but the Host header will be myurl.com:443, resulting in the error rpc error: code = Unimplemented desc =. If you run into this issue, there are two ways to solve it depending on your use case, both using the Module resource.

The first is to set the strip_matching_host_port property to true. However, this only works if the port in the header matches the port that Envoy listens on (8443 by default). In the default installation of Ambassador Edge Stack, the public port is 443, which then maps internally to 8443, so this only works for custom installations where the public service port matches the port in the Listener resource.

The second solution is to use the following Lua script, which always strips the port:

Originating TLS with gRPC service

Ambassador Edge Stack can originate TLS with your gRPC service so the entire RPC channel is encrypted. To configure this, first get some TLS certificates and configure the server to open a secure channel with them. Using self-signed certs this can be done with OpenSSL and adding a couple of lines to the server code.

Rebuild your docker container making sure the certificates are included and follow the same steps of testing and deploying to Kubernetes. You will need to make a small change to the client code to test locally.

Once deployed we will need to tell Ambassador Edge Stack to originate TLS to the application.

We need to tell Ambassador Edge Stack to route to the service: over https and have the service listen on 443. We also need to tell Ambassador Edge Stack to use ALPN protocols when originating TLS with the application, the same way we did with TLS termination. This is done by setting alpn_protocols: ["h2"] in a TLSContext telling the service to use that tls-context in the mapping by setting tls: upstream.

Refer to the TLS document for more information on TLS origination.

gRPC headers

gRPC services use HTTP/2 headers. This means that some header-based routing rules will need to be rewritten to support HTTP/2 headers. For example, host: subdomain.host.com needs to be rewritten using the headers: attribute with the :authority header:

Note

Ingress controllers

Some Kubernetes ingress controllers do not support HTTP/2 fully. As a result, if you are running Ambassador Edge Stack with an ingress controller in front, you may find that gRPC requests fail even with correct Ambassador Edge Stack configuration.

A simple way around this is to use Ambassador Edge Stack with a LoadBalancer service, rather than an Ingress controller. You can also consider using Ambassador Edge Stack as your Ingress Controller.

Mappings with hosts

As with any Mapping, your gRPC service's Mapping may include a host:

Some gRPC client libraries produce requests where the host or :authority header includes the port number. For example, a request to the above service might include host: api.example.com:443 instead of just host: api.example.com. To avoid having Ambassador Edge Stack return a 404 (not found) response to these requests due to the mismatched host, you may want to set strip_matching_host_port in the Ambassador module.

Alternately, you may find it cleaner to make sure your gRPC client does not include the port in the host header. Here is an example using gRPC/Go.

gRPC-Web

Ambassador Edge Stack also supports the gRPC-Web protocol for browser-based gRPC applications.