Application Protocol Selection
Kubernetes services expose one or more ports. A port exposed by an application running the service can serve a specific application protocol such as HTTP, TCP etc. There is a requirement to be able to determine the application protocol served by a service’s port to be able to correctly configure protocol specific configurations in Envoy (Filters, Routes, RBAC policies). Prior to Kubernetes 1.19, there is no way to determine the application protocol for a port. The IP
protocol field on the Service resource must be one of TCP, UDP, or SCTP, so this cannot be used to determine the application protocols such HTTP, gRPC etc. To address this limitation, Kubernetes 1.19 introduced an
AppProtocol field for the Service resource.
This document proposes to leverage the newly introduced
AppProtocol field to determine the application protocol for a service’s port in OSM. The application protocol on the port will be used to infer the protocol of the inbound traffic received on that port by the upstream proxy. Based on the protocol detected, appropriate filer chains will be configured on the upstream proxy to apply protocol specific filters to handle protocol specific policies.
AppProtocol can be specified by default in Kubernetes server versions >= v1.19. In older versions where this field cannot be set, the application protocol for a service port can be indicated by prefixing the protocol name as a part of the port name. If the application protocol cannot be derived, OSM controller will use
http as the default application protocol for a port.
*Note that for port field in the service spec, the
AppProtocol field takes precedence over the
Name field if both are specified.
Consider the following SMI traffic access and traffic specs policies:
tcp-routethat specifies the port TCP traffic should be allowed on.
http-routethat specifies the HTTP routes for which HTTP traffic should be allowed.
testthat allows pods in the service account
sa-2to access pods in the service account
sa-1for the speficied TCP and HTTP rules.
- name: version
name: sa-1 # There are 2 services under this service account: service-1 and service-2
- kind: TCPRoute
- kind: HTTPRouteGroup
- kind: ServiceAccount
Kubernetes service resources should explicitly specify the application protocol being served by the service’s ports using the
service-1 backed by a pod in service account
http application traffic should be defined as follows:
- port: 8080
service-2 backed by a pod in service account
sa-1 serving raw
tcp application traffic shold be defined as follows:
- port: 8080
If the cluster is using an older Kubernetes version where
appProtocol cannot be specified in the Service spec, the application protocol can be indicated by prefixing the port name with the protocol as follows:
- port: 80
name: http-someport # prefix 'http-' indicates http application protocol
- port: 90
name: tcp-someport # prefix 'tcp-' indicates tcp application protocol
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