Protocol Selection

Istio supports proxying any TCP traffic. This includes HTTP, HTTPS, gRPC, as well as raw TCP protocols. In order to provide additional capabilities, such as routing and rich metrics, the protocol must be determined. This can be done automatically or explicitly specified.

Non-TCP based protocols, such as UDP, are not proxied. These protocols will continue to function as normal, without any interception by the Istio proxy but cannot be used in proxy-only components such as ingress or egress gateways.

Automatic protocol selection

Istio can automatically detect HTTP and HTTP/2 traffic. If the protocol cannot automatically be determined, traffic will be treated as plain TCP traffic.

The following protocols are known to be incompatible with automatic protocol selection, and must be explicitly declared or they will be treated as TCP:

Server first protocols

Some protocols are “Server First” protocols, which means the server will send the first bytes. In these cases, automatic protocol detection will not function correctly, as Istio will determine the protocol based on the initial bytes. If you are using a server first protocol, you should follow the explicit protocol selection instructions, below, to declare the protocol.

Explicit protocol selection

Protocols can be specified manually in the Service definition.

This can be configured in two ways:

• By the name of the port: name: <protocol>[-<suffix>].
• In Kubernetes 1.18+, by the appProtocol field: appProtocol: <protocol>.

The following protocols are supported:

• http
• http2
• https
• tcp
• tls
• grpc
• grpc-web
• mongo
• mysql*
• redis*
• udp (UDP will not be proxied, but the port can be explicitly declared as UDP)

* These protocols are disabled by default to avoid accidentally enabling experimental features. To enable them, configure the corresponding Pilot environment variables.

Below is an example of a Service that defines a mysql port by appProtocol and an http port by name:

kind: Service
metadata:
  name: myservice
spec:
  ports:
  - number: 3306
    name: database
    appProtocol: mysql
  - number: 80
    name: http-web