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Virtual Outbound
This policy lets you customize hostnames and ports for communicating with data plane proxies.
Possible use cases are:
1) Preserving hostnames when migrating to service mesh. 2) Providing multiple hostnames for reaching the same service, for example when renaming or for usability. 3) Providing specific routes, for example to reach a specific pod in a service with StatefulSets on Kubernetes, or to add a URL to reach a specific version of a service. 4) Expose multiple inbounds on different ports.
Limitations:
- Complex virtual outbounds do not work for cross-zone traffic. This is because only service tags are propagated across zones.
- When duplicate
(hostname, port)
combinations are detected, the virtual outbound with the highest priority takes over. For more information, see the documentation on how Kong Mesh chooses the right policy. All duplicate instances are logged.
conf.host
and conf.port
are processed as go text templates with a key-value pair derived from conf.parameters
.
conf.selectors
are used to specify which proxies this policy applies to.
For example a proxy with this definition:
type: Dataplane
mesh: default
name: backend-1
networking:
address: 192.168.0.2
inbound:
- port: 9000
servicePort: 6379
tags:
kuma.io/service: backend
version: v1
port: 1800
and a virtual outbound with this definition:
type: VirtualOutbound
mesh: default
name: test
selectors:
- match:
kuma.io/service: "*"
conf:
host: "{{.v}}.{{.service}}.mesh"
port: "{{.port}}"
parameters:
- name: service
tagKey: "kuma.io/service"
- name: port
tagKey: port
- name: v
tagKey: version
produce the hostname: v1.backend.mesh
with port: 1800
.
Additional requirements:
- Transparent proxy.
- Either data plane proxy DNS, or else the value of
conf.host
must end with the value ofdns_server.domain
(default value.mesh
). -
name
must be alphanumeric. (Used as a go template key). - Each value of
name
must be unique. -
kuma.io/service
must be specified even if it’s unused in the template. (Prevents defining hostnames that spans services).
The default value of tagKey
is the value of name
.
For each virtual outbound, the Kong Mesh control plane processes all data plane proxies that match the selector.
It then applies the templates for conf.host
and conf.port
and assigns a virtual IP address for each hostname.
Examples
The following examples show how to use virtual outbounds for different use cases.
Same as the default DNS
One hostname per version
Custom tag to define the hostname and port
One hostname per instance
Enables reaching specific data plane proxies for a service. Useful for running distributed databases such as Kafka or Zookeeper.