Traffic Management

Deployment and Configuration Guidelines

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

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 in Istio 1.0.1, an experimental feature has been added to 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.

503 errors after setting destination rule

If requests to a service immediately start generating HTTP 503 errors after you applied a DestinationRule and the errors continue until you remove or revert the DestinationRule, then the DesintationRule is probably causing a TLS conflict for the service.

For example, if you configure mutual TLS in the cluster globally, the DestinationRule must include the following trafficPolicy:

trafficPolicy:
  tls:
    mode: ISTIO_MUTUAL

Otherwise, the mode defaults to DISABLED causing client proxy sidecars to make plain HTTP requests instead of TLS encrypted requests. Thus, the requests conflict with the server proxy because the server proxy expects encrypted requests.

To confirm there is a conflict, check whether the STATUS field in the output of the istioctl authn tls-check command is set to CONFLICT for your service. For example:

$ istioctl authn tls-check httpbin.default.svc.cluster.local
HOST:PORT                                  STATUS       SERVER     CLIENT     AUTHN POLICY     DESTINATION RULE
httpbin.default.svc.cluster.local:8000     CONFLICT     mTLS       HTTP       default/         httpbin/default

Whenever you apply a DestinationRule, ensure the trafficPolicy TLS mode matches the global server configuration.

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.

Route rules have no effect on ingress gateway requests

Let's assume you are using an ingress Gateway and corresponding VirtualSerive to access an internal service. For example, your VirtualService looks something like this:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: myapp
spec:
  hosts:
  - "myapp.com" # or maybe "*" if you are testing without DNS using the ingress-gateway IP (e.g., http://1.2.3.4/hello)
  gateways:
  - myapp-gateway
  http:
  - match:
    - uri:
        prefix: /hello
    route:
    - destination:
        host: helloworld.default.svc.cluster.local
  - match:
    ...

You also have a VirtualService which routes traffic for the helloworld service to a particular subset:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: helloworld
spec:
  hosts:
  - helloworld.default.svc.cluster.local
  http:
  - route:
    - destination:
        host: helloworld.default.svc.cluster.local
        subset: v1

In this situation you will notice that requests to the helloworld service via the ingress gateway will not be directed to subset v1 but instead will continue to use default round-robin routing.

The ingress requests are using the gateway host (e.g., myapp.com) which will activate the rules in the myapp VirtualService that routes to any endpoint in the helloworld service. Internal requests with the host helloworld.default.svc.cluster.local will use the helloworld VirtualService which directs traffic exclusively to subset v1.

To control the traffic from the gateway, you need to include the subset rule in the myapp VirtualService:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: myapp
spec:
  hosts:
  - "myapp.com" # or maybe "*" if you are testing without DNS using the ingress-gateway IP (e.g., http://1.2.3.4/hello)
  gateways:
  - myapp-gateway
  http:
  - match:
    - uri:
        prefix: /hello
    route:
    - destination:
        host: helloworld.default.svc.cluster.local
        subset: v1
  - match:
    ...

Alternatively, you can combine both VirtualServices into one unit if possible:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: myapp
spec:
  hosts:
  - myapp.com # cannot use "*" here since this is being combined with the mesh services
  - helloworld.default.svc.cluster.local
  gateways:
  - mesh # applies internally as well as externally
  - myapp-gateway
  http:
  - match:
    - uri:
        prefix: /hello
      gateways:
      - myapp-gateway #restricts this rule to apply only to ingress gateway
    route:
    - destination:
        host: helloworld.default.svc.cluster.local
        subset: v1
  - match:
    - gateways:
      - mesh # applies to all services inside the mesh
    route:
    - destination:
        host: helloworld.default.svc.cluster.local
        subset: v1

Route rules have no effect on my application

If route rules are working perfectly for the Bookinfo sample, but similar version routing rules have no effect on your own application, it may be that your Kubernetes services need to be changed slightly.

Kubernetes services must adhere to certain restrictions in order to take advantage of Istio's L7 routing features. Refer to the Requirements for Pods and Services for details.

Envoy won't connect to my HTTP/1.0 service

Envoy requires HTTP/1.1 or HTTP/2 traffic for upstream services. For example, when using NGINX for serving traffic behind Envoy, you will need to set the proxy_http_version directive in your NGINX configuration to be “1.1”, since the NGINX default is 1.0.

Example configuration:

upstream http_backend {
    server 127.0.0.1:8080;

    keepalive 16;
}

server {
    ...

    location /http/ {
        proxy_pass http://http_backend;
        proxy_http_version 1.1;
        proxy_set_header Connection "";
        ...
    }
}

Headless TCP services losing connection

If istio-citadel is deployed, Envoy is restarted every 15 minutes to refresh certificates. This causes the disconnection of TCP streams or long-running connections between services.

You should build resilience into your application for this type of disconnect, but if you still want to prevent the disconnects from happening, you will need to disable mutual TLS and the istio-citadel deployment.

First, edit your istio configuration to disable mutual TLS:

$ kubectl edit configmap -n istio-system istio
$ kubectl delete pods -n istio-system -l istio=pilot

Next, scale down the istio-citadel deployment to disable Envoy restarts:

$ kubectl scale --replicas=0 deploy/istio-citadel -n istio-system

This should stop Istio from restarting Envoy and disconnecting TCP connections.

Configuring multiple TLS hosts in a gateway

If you configure multiple gateway servers, either in a single Gateway, or spread across more than one that use the same selector labels, with the same port number and protocol HTTPS, then you must ensure that the corresponding port names are unique. For example:

cat <<EOF | kubectl apply -f -
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-httpbin
      protocol: HTTPS
    tls:
      mode: SIMPLE
      serverCertificate: /etc/istio/ingressgateway-certs/tls.crt
      privateKey: /etc/istio/ingressgateway-certs/tls.key
    hosts:
    - "httpbin.example.com"
  - port:
      number: 443
      name: https-bookinfo
      protocol: HTTPS
    tls:
      mode: SIMPLE
      serverCertificate: /etc/istio/ingressgateway-bookinfo-certs/tls.crt
      privateKey: /etc/istio/ingressgateway-bookinfo-certs/tls.key
    hosts:
    - "bookinfo.com"
EOF

If the port names are not unique, istio-pilot will return the following error in the log:

port https.443.HTTPS: non unique port name for HTTPS port

If you run a curl command, command returns 0 and print SSL_SYSCALL_ERROR.


Debugging Envoy and Pilot

Introduction to Network Operations