Routing HTTP/2 and gRPC traffic to apps

Here are instructions for routing HTTP/2 and gRPC traffic to VMware Tanzu Application Service for VMs (TAS for VMs) apps. HTTP/2 is the second major version of the the HTTP protocol. In TAS for VMs v2.12 and later, HTTP/2 support is enabled by default.

For more information about the HTTP/2 protocol, see RFC 7540.

gRPC is a Remote Procedure Call (RPC) framework that uses HTTP/2 as its transport medium. It is especially useful for managing communication between apps in a microservices cluster. For apps to serve gRPC traffic, every network hop between the client and app must use HTTP/2.

For more information, see gRPC.

Performance

HTTP/2 can provide performance improvements for apps that are built to do the following:

Load many resources in parallel. For example, an HTML page that loads many images or JavaScript files.
Use large and repetitive headers.

Other apps might see minimal or no performance increases. Experiment with your app to see how serving HTTP/2 affects its performance.

For an example of an app that benefits from HTTP/2, see the Cloud Foundry HTTP/2 Tile Demo App.

Limitations

HTTP/2 support in TAS for VMs has the following limitations:

End-to-end HTTP/2 is not available for Windows Diego Cells. Routes with HTTP/2 mappings continue to send HTTP/1.1 traffic to apps that run on Windows Diego Cells.
Routes that have route services bound to them might not support end-to-end HTTP/2 depending on what protocols the bound service supports. For more information, see Route Services.

How pushing apps with HTTP/2 works

This section describes how pushing apps with HTTP/2 works.

If your TAS for VMs deployment is configured to support HTTP/2, then all traffic ingressing to TAS for VMs supports HTTP/2. The traffic is forwarded as HTTP/1.1 before it reaches your app unless configured otherwise.

For more information, see Configuring HTTP/2 Support.

To serve gRPC traffic, your app must use HTTP/2 for all network hops. Configure your route to send HTTP/2 traffic to your app. When configured, traffic that matches the route is always sent to your app over HTTP/2 regardless of the original ingress protocol.

For example, external HTTP/1.1 requests are forwarded to your app over HTTP/2. Your app does not have the opportunity to negotiate what protocol it receives.

Note If a client is familiar with the HTTP/2 specification, your app receives HTTP/2 with prior knowledge. For more information, see Starting HTTP/2 with Prior Knowledge in RFC 7540: Hypertext Transfer Protocol Version 2 (HTTP/2).

Push apps with HTTP/2 support

This section describes how to push TAS for VMs apps with support for HTTP/2.

You do not need to make changes to existing apps to support HTTP/2. For information about pushing an HTTP/1.1 app that serves HTTP/2 traffic, see Push an HTTP/1.1 App that Serves HTTP/2.

There are multiple ways to push an app with end-to-end HTTP/2. You can push the app using either the app manifest or the Cloud Foundry Command Line Interface (cf CLI). You can also use either method to push an app that serves gRPC traffic.

To push an app with end-to-end HTTP/2, see the following sections:

Push an App with End-to-End HTTP/2 Using the App Manifest
Push an App with End-to-End HTTP/2 Using the cf CLI
Push a gRPC App

Push an HTTP/1.1 app that serves HTTP/2

To push an HTTP/1.1 app that can serve HTTP/2 traffic:

Push the HTTP/1.1 app by running:
```
cf push MY-APP
```
Where MY-APP is the name of your app.
Send an HTTP/2 request to the app by running:
```
curl MY-APP.EXAMPLE.COM --http2 -v
```
Where MY-APP.EXAMPLE.COM is the route mapped to your app.

The request and response are both issued over HTTP/2.

Note To issue this request, you must use a version of curl that supports HTTP/2.
Review the app logs by running:
```
cf logs MY-APP
```
The request to the app is issued over HTTP/1.1.

Push an app with End-to-End HTTP/2 using the app manifest

To push an app that serves HTTP/2 traffic using the app manifest:

Use an app that supports serving HTTP/2 traffic with prior knowledge. For example, you can use the HTTP/2 test app from Cloud Foundry Acceptance Tests on GitHub.
Create an app manifest named manifest.yml with a route mapped to the app with HTTP/2:
```
---
applications:
- name: MY-APP
  routes:
    - route: MY-APP.EXAMPLE.COM
      protocol: http2
```
Where MY-APP is the name of your app and MY-APP.EXAMPLE.COM is the route you want to map to your app.
Push the app with the manifest by running:
```
cf push -f manifest.yml
```
Send an HTTP/2 request to the app by running:
```
curl MY-APP.EXAMPLE.COM --http2 -v
```
The request and response are both sent over HTTP/2. The response from the test app includes the protocol.

For example:
```
Hello, /, TLS: false, Protocol: HTTP/2.0
```
The response shows that the request was received over HTTP/2.

Push an app with end-to-end HTTP/2 using the cf CLI

The recommended way to do this is using the routes attribute in the manifest YAML file.

Important The following procedure is supported only for cf CLI v6; the `--hostname` flag is deprecated in cf CLI v7.

To push an app that serves HTTP/2 traffic using the cf CLI (v6 only):

Use an app that supports serving HTTP/2 traffic with prior knowledge. For example, you can use the HTTP/2 test app from Cloud Foundry Acceptance Tests on GitHub.
Push the app without a default route by running with the --no-route flag. Note that this flag is no longer unbinds all existing routes associated with the app.
```
cf push --no-route
```
You can map a route by running:
```
cf map-route MY-APP EXAMPLE.COM --hostname host
```
Where MY-APP is the name of your app and EXAMPLE.COM is the route you want to map to your app.
Send an HTTP/2 request to the app by running:
```
curl HOST.EXAMPLE.COM --http2 -v
```
The request and response are both sent over HTTP/2. The response from the test app includes the protocol.

For example:
```
Hello, /, TLS: false, Protocol: HTTP/2.0
```
The response shows that the request was received over HTTP/2.

Push a gRPC app

To push an app that serves gRPC traffic:

Use an app that supports serving gRPC traffic. For example, you can use the gRPC test app from Cloud Foundry Acceptance Tests on GitHub.
Push the app with HTTP/2 activated using either the app manifest or the cf CLI. See Push an App with End-to-End HTTP/2 Using the App Manifest or Push an App with End-to-End HTTP/2 Using the cf CLI.
Send a gRPC request to the app using grpcurl by running the following command. For more information, see grpcurl.
```
grpcurl -vv -import-path ./test/ -proto test.proto MY-APP.EXAMPLE.COM:443 test.Test.Run
```
Where MY-APP.EXAMPLE.COM is the route to your app.

A successful response looks like the following:
```
Response contents:
{
  "body": "Hello"
}
```

Sample applications

Here are some sample HTTP/2 and gRPC applications from the community. They can be used to experiment with HTTP/2 and provide code examples for different languages and frameworks.