README-host-in-multiple-vs.md

VirtualServices Define the Same Host

Example

ERROR: The VirtualServices vs1.default, vs2.default with routes /foo prefix /foo exact define the same host (*) and conflict. A Virtual Service defining the same host must not conflict. Consider updating the VirtualServices to have unique hostnames or update the rules so they do not conflict.

Description

Istio requires that all hostnames defined by VirtualServices in your cluster are unique. Short hostnames (those that do not contain a '.') are converted to fully qualified domain names (FQDN) that include the namespace where the VirtualService resource is defined, so short hostnames are allowed to be repeated so long as they are defined in separate namespaces. Converting short names to FQDN does not apply to hostnames that include a wildcard '*' prefix, IP addresses, or web addresses. These must be unique regardless of the namespace in which they are defined.

Conflicting Hostnames Samples

Sample 1

The FQDNs assigned to the hosts below would be reviews.foo.svc.cluster.local and reviews.bar.svc.cluster.local respectively. They use the same gateway "my-gateway-1". This is allowed.

  apiVersion: networking.istio.io/v1beta1
  kind: VirtualService
  metadata:
    name: vs1
    namespace: foo
  spec:
    hosts:
    - reviews
    gateways:
    - my-gateway-1
    ...
---
  apiVersion: networking.istio.io/v1beta1
  kind: VirtualService
  metadata:
    name: vs2
    namespace: bar
  spec:
    hosts:
    - reviews
    gateways:
    - my-gateway-1
    ...

Sample 2

The FQDNs assigned to the hosts in the following example would both be reviews.default.svc.cluster.local, and their matching rules conflict (since /service1 is a prefix of /service1/start). This is not allowed, and will cause indeterminate routing behavior in your cluster.

  apiVersion: networking.istio.io/v1beta1
  kind: VirtualService
  metadata:
    name: vs3
    namespace: default
  spec:
    hosts:
    - reviews
    gateways:
    - my-gateway-1
    http:
      - match:
        - uri:
          prefix: /service1
---
  apiVersion: networking.istio.io/v1beta1
  kind: VirtualService
  metadata:
    name: vs4
    namespace: default
  spec:
    hosts:
    - reviews
    gateways:
    - my-gateway-1
    http:
      - match:
        - uri:
          prefix: /service1/start

The following note will be generated:

Summary: "Multiple VirtualServices define the same host (reviews) and conflict"

Message: "ERROR: The VirtualServices vs3.default, vs4.default define the same host (reviews)
matching uris /service1 prefix /service1/start prefix conflict. VirtualServices defining the same
host must not conflict. Considuring updating the VirtualServices to have unique hostnames or update the
rules so they do not conflict."

See Suggested Resolution (1) below for an example of how to fix this by changing the hostnames and gateways to be unique.

Sample 3

The following sample is also not allowed, as it defines the same web address in two different VirtualService resources. This will also cause indeterminate routing behavior in your cluster.

  apiVersion: networking.istio.io/v1beta1
  kind: VirtualService
  metadata:
    name: vs5
    namespace: foo
  spec:
    gateways:
    - my-gateway-1
    hosts:
    - google.com
    http:
    - match:
      - uri:
          prefix: /search
      route:
      - destination:
          host: search.foo.svc.cluster.local
---
  apiVersion: networking.istio.io/v1beta1
  kind: VirtualService
  metadata:
    name: vs6
    namespace: foo
  spec:
    gateways:
    - my-gateway-1
    hosts:
    - google.com
    http:
    - match:
      - uri:
          exact: /search
      route:
      - destination:
          host: mail.foo.svc.cluster.local

The following note will be generated:

Summary: "Multiple VirtualServices define the same host (google.com) and
gateway (my-gateway-1)"

Message: "ERROR: The VirtualServices vs5.foo, vs6.foo  define the same host
matching uris (/search prefix /search exact) conflict. VirtualServices defining the same
host must not conflict. Considuring updating the VirtualServices to have unique hostnames or update the
rules so they do not conflict."

See Suggested Resolution (2) below for an example of how to fix this by merging the rules of the two VirtualService resources into one VirtualService resource.

Suggested Resolution

You can do one of these two things:

1. Make the hostnames unique. Change the hostnames defined in the conflicting VirtualServices to be unique. The following VirtualServices have unique hostnames "reviews" and "ratings".

    apiVersion: networking.istio.io/v1beta1
    kind: VirtualService
    metadata:
      name: vs3
      namespace: default
    spec:
      gateways:
      - my-gateway-1
      hosts:
      - reviews
      ...
    ---
    apiVersion: networking.istio.io/v1beta1
    kind: VirtualService
    metadata:
      name: vs4
      namespace: default
    spec:
      gateways:
      - my-gateway-1
      hosts:
      - ratings
      ...