Deployment and Configuration Guidelines

This section provides specific deployment or configuration guidelines to avoid networking or traffic management issues.

Configuring multiple TLS hosts in a gateway

If you apply a Gateway configuration that has the same selector labels as another existing Gateway, then if they both expose the same HTTPS port you must ensure that they have unique port names. Otherwise, the configuration will be applied without an immediate error indication but it will be ignored in the runtime gateway configuration. For example:

apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: mygateway
spec:
  selector:
    istio: ingressgateway # use istio default ingress gateway
  servers:
  - port:
      number: 443
      name: https
      protocol: HTTPS
    tls:
      mode: SIMPLE
      serverCertificate: /etc/istio/ingressgateway-certs/tls.crt
      privateKey: /etc/istio/ingressgateway-certs/tls.key
    hosts:
    - "myhost.com"
---
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: mygateway2
spec:
  selector:
    istio: ingressgateway # use istio default ingress gateway
  servers:
  - port:
      number: 443
      name: https
      protocol: HTTPS
    tls:
      mode: SIMPLE
      serverCertificate: /etc/istio/ingressgateway-certs/tls.crt
      privateKey: /etc/istio/ingressgateway-certs/tls.key
    hosts:
    - "myhost2.com"

With this configuration, requests to the second host, myhost2.com, will fail because both gateway ports have name: https. A curl request, for example, will produce an error message something like this:

curl: (35) LibreSSL SSL_connect: SSL_ERROR_SYSCALL in connection to myhost2.com:443

You can confirm that this has happened by checking Pilot’s logs for a message similar to the following:

$ kubectl logs -n istio-system $(kubectl get pod -l istio=pilot -n istio-system -o jsonpath={.items..metadata.name}) -c discovery | grep "non unique port"
2018-09-14T19:02:31.916960Z info    model   skipping server on gateway mygateway2 port https.443.HTTPS: non unique port name for HTTPS port

To avoid this problem, ensure that multiple uses of the same protocol: HTTPS port are uniquely named. For example, change the second one to https2:

apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: mygateway2
spec:
  selector:
    istio: ingressgateway # use istio default ingress gateway
  servers:
  - port:
      number: 443
      name: https2
      protocol: HTTPS
    tls:
      mode: SIMPLE
      serverCertificate: /etc/istio/ingressgateway-certs/tls.crt
      privateKey: /etc/istio/ingressgateway-certs/tls.key
    hosts:
    - "myhost2.com"

Multiple virtual services and destination rules for the same host

In situations where it is inconvenient to define the complete set of route rules or policies for a particular host in a single VirtualService or DestinationRule resource, it may be preferable to incrementally specify the configuration for the host in multiple resources. Starting with Istio 1.0.1, Pilot will merge such destination rules and merge such virtual services if they are bound to a gateway.

Consider the case of a VirtualService bound to an ingress gateway exposing an application host which uses path-based delegation to several implementation services, something like this:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: myapp
spec:
  hosts:
  - myapp.com
  gateways:
  - myapp-gateway
  http:
  - match:
    - uri:
        prefix: /service1
    route:
    - destination:
        host: service1.default.svc.cluster.local
  - match:
    - uri:
        prefix: /service2
    route:
    - destination:
        host: service2.default.svc.cluster.local
  - match:
    ...

The downside of this kind of configuration is that other configuration (e.g., route rules) for any of the underlying microservices, will need to also be included in this single configuration file, instead of in separate resources associated with, and potentially owned by, the individual service teams. See Route rules have no effect on ingress gateway requests for details.

To avoid this problem, it may be preferable to break up the configuration of myapp.com into several VirtualService fragments, one per backend service. For example:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: myapp-service1
spec:
  hosts:
  - myapp.com
  gateways:
  - myapp-gateway
  http:
  - match:
    - uri:
        prefix: /service1
    route:
    - destination:
        host: service1.default.svc.cluster.local
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: myapp-service2
spec:
  hosts:
  - myapp.com
  gateways:
  - myapp-gateway
  http:
  - match:
    - uri:
        prefix: /service2
    route:
    - destination:
        host: service2.default.svc.cluster.local
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: myapp-...

When a second and subsequent VirtualService for an existing host is applied, istio-pilot will merge the additional route rules into the existing configuration of the host. There are, however, several caveats with this feature that must be considered carefully when using it.

  1. Although the order of evaluation for rules in any given source VirtualService will be retained, the cross-resource order is UNDEFINED. In other words, there is no guaranteed order of evaluation for rules across the fragment configurations, so it will only have predictable behavior if there are no conflicting rules or order dependency between rules across fragments.
  2. There should only be one “catch-all” rule (i.e., a rule that matches any request path or header) in the fragments. All such “catch-all” rules will be moved to the end of the list in the merged configuration, but since they catch all requests, whichever is applied first will essentially override and disable any others.
  3. A VirtualService can only be fragmented this way if it is bound to a gateway. Host merging is not supported in sidecars.

A DestinationRule can also be fragmented with similar merge semantic and restrictions.

  1. There should only be one definition of any given subset across multiple destination rules for the same host. If there is more than one with the same name, the first definition is used and any following duplicates are discarded. No merging of subset content is supported.
  2. There should only be one top-level trafficPolicy for the same host. When top-level traffic policies are defined in multiple destination rules, the first one will be used. Any following top-level trafficPolicy configuration is discarded.
  3. Unlike virtual service merging, destination rule merging works in both sidecars and gateways.

Avoid 503 errors while reconfiguring service routes

When setting route rules to direct traffic to specific versions (subsets) of a service, care must be taken to ensure that the subsets are available before they are used in the routes. Otherwise, calls to the service may return 503 errors during a reconfiguration period.

Creating both the VirtualServices and DestinationRules that define the corresponding subsets using a single kubectl call (e.g., kubectl apply -f myVirtualServiceAndDestinationRule.yaml is not sufficient because the resources propagate (from the configuration server, i.e., Kubernetes API server) to the Pilot instances in an eventually consistent manner. If the VirtualService using the subsets arrives before the DestinationRule where the subsets are defined, the Envoy configuration generated by Pilot would refer to non-existent upstream pools. This results in HTTP 503 errors until all configuration objects are available to Pilot.

To make sure services will have zero down-time when configuring routes with subsets, follow a “make-before-break” process as described below:

  • When adding new subsets:

    1. Update DestinationRules to add a new subset first, before updating any VirtualServices that use it. Apply the rule using kubectl or any platform-specific tooling.

    2. Wait a few seconds for the DestinationRule configuration to propagate to the Envoy sidecars

    3. Update the VirtualService to refer to the newly added subsets.

  • When removing subsets:

    1. Update VirtualServices to remove any references to a subset, before removing the subset from a DestinationRule.

    2. Wait a few seconds for the VirtualService configuration to propagate to the Envoy sidecars.

    3. Update the DestinationRule to remove the unused subsets.

Browser problem when multiple gateways configured with same TLS certificate

Configuring more than one gateway using the same TLS certificate will cause browsers that leverage HTTP/2 connection reuse (i.e., most browsers) to produce 404 errors when accessing a second host after a connection to another host has already been established.

For example, let’s say you have 2 hosts that share the same TLS certificate like this:

  • Wildcard certificate *.test.com installed in istio-ingressgateway
  • Gateway configuration gw1 with host service1.test.com, selector istio: ingressgateway, and TLS using gateway’s mounted (wildcard) certificate
  • Gateway configuration gw2 with host service2.test.com, selector istio: ingressgateway, and TLS using gateway’s mounted (wildcard) certificate
  • VirtualService configuration vs1 with host service1.test.com and gateway gw1
  • VirtualService configuration vs2 with host service2.test.com and gateway gw2

Since both gateways are served by the same workload (i.e., selector istio: ingressgateway) requests to both services (service1.test.com and service2.test.com) will resolve to the same IP. If service1.test.com is accessed first, it will return the wildcard certificate (*.test.com) indicating that connections to service2.test.com can use the same certificate. Browsers like Chrome and Firefox will consequently reuse the existing connection for requests to service2.test.com. Since the gateway (gw1) has no route for service2.test.com, it will then return a 404 (Not Found) response.

You can avoid this problem by configuring a single wildcard Gateway, instead of two (gw1 and gw2). Then, simply bind both VirtualServices to it like this:

  • Gateway configuration gw with host *.test.com, selector istio: ingressgateway, and TLS using gateway’s mounted (wildcard) certificate
  • VirtualService configuration vs1 with host service1.test.com and gateway gw
  • VirtualService configuration vs2 with host service2.test.com and gateway gw