Networking Problems

Requests are rejected by Envoy

Requests may be rejected for various reasons. The best way to understand why requests are being rejected isby inspecting Envoy’s access logs. By default, access logs are output to the standard output of the container.Run the following command to see the log:

  1. $ kubectl logs PODNAME -c istio-proxy -n NAMESPACE

In the default access log format, Envoy response flags and Mixer policy status are located after the response code,if you are using a custom log format, make sure to include %RESPONSE_FLAGS% and %DYNAMIC_METADATA(istio.mixer:status)%.

Refer to the Envoy response flagsfor details of response flags.

Common response flags are:

  • NR: No route configured, check your DestinationRule or VirtualService.
  • UO: Upstream overflow with circuit breaking, check your circuit breaker configuration in DestinationRule.
  • UF: Failed to connect to upstream, if you’re using Istio authentication, check for amutual TLS configuration conflict.A request is rejected by Mixer if the response flag is UAEX and the Mixer policy status is not -.

Common Mixer policy statuses are:

  • UNAVAILABLE: Envoy cannot connect to Mixer and the policy is configured to fail close.
  • UNAUTHENTICATED: The request is rejected by Mixer authentication.
  • PERMISSION_DENIED: The request is rejected by Mixer authorization.
  • RESOURCE_EXHAUSTED: The request is rejected by Mixer quota.
  • INTERNAL: The request is rejected due to Mixer internal error.

Route rules don’t seem to affect traffic flow

With the current Envoy sidecar implementation, up to 100 requests may be required for weightedversion distribution to be observed.

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 thatyour Kubernetes services need to be changed slightly.Kubernetes services must adhere to certain restrictions in order to take advantage ofIstio’s L7 routing features.Refer to the [Requirements for Pods and Services]/docs/ops/prep/requirements/)for details.

Another potential issue is that the route rules may simply be slow to take effect.The Istio implementation on Kubernetes utilizes an eventually consistentalgorithm to ensure all Envoy sidecars have the correct configurationincluding all route rules. A configuration change will take some timeto propagate to all the sidecars. With large deployments thepropagation will take longer and there may be a lag time on theorder of seconds.

Destination rule policy not activated

Although destination rules are associated with a particular destination host,the activation of subset-specific policies depends on route rule evaluation.

When routing a request, Envoy first evaluates route rules in virtual servicesto determine if a particular subset is being routed to.If so, only then will it activate any destination rule policies corresponding to the subset.Consequently, Istio only applies the policies you define for specific subsets ifyou explicitly routed traffic to the corresponding subset.

For example, consider the following destination rule as the one and only configuration defined for thereviews service, that is, there are no route rules in a corresponding VirtualService definition:

  1. apiVersion: networking.istio.io/v1alpha3
  2. kind: DestinationRule
  3. metadata:
  4.   name: reviews
  5. spec:
  6.   host: reviews
  7.   subsets:
  8.   - name: v1
  9.     labels:
  10.       version: v1
  11.     trafficPolicy:
  12.       connectionPool:
  13.         tcp:
  14.           maxConnections: 100

Even if Istio’s default round-robin routing calls “v1” instances on occasion,maybe even always if “v1” is the only running version, the above traffic policy will never be invoked.

You can fix the above example in one of two ways:

  • Move the traffic policy in the destination rule up a level to make the policyapply to any subset, for example:
  1. apiVersion: networking.istio.io/v1alpha3
  2. kind: DestinationRule
  3. metadata:
  4.   name: reviews
  5. spec:
  6.   host: reviews
  7.   trafficPolicy:
  8.     connectionPool:
  9.       tcp:
  10.         maxConnections: 100
  11.   subsets:
  12.   - name: v1
  13.     labels:
  14.       version: v1
  • Define proper route rules for the service using a VirtualService.For example, add a simple route rule for the v1 subset of the reviews service:
  1. apiVersion: networking.istio.io/v1alpha3
  2. kind: VirtualService
  3. metadata:
  4.   name: reviews
  5. spec:
  6.   hosts:
  7.   - reviews
  8.   http:
  9.   - route:
  10.     - destination:
  11.         host: reviews
  12.         subset: v1

The default Istio behavior conveniently sends traffic from any sourceto all versions of the destination service without you setting any rules.As soon as you need to differentiate between the versions of a service,you need to define routing rules.Due to this fact, we consider a best practice to set a default routing rulefor every service from the start.

503 errors after setting destination rule

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

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

  1. trafficPolicy:
  2.   tls:
  3.     mode: ISTIO_MUTUAL

Otherwise, the mode defaults to DISABLE causing client proxy sidecars to make plain HTTP requestsinstead of TLS encrypted requests. Thus, the requests conflict with the server proxy because the server proxy expectsencrypted requests.

To confirm there is a conflict, check whether the STATUS field in the output of the istioctl authn tls-check commandis set to CONFLICT for your service. For example, a command similar to the following could be used to checkfor a conflict with the httpbin service:

  1. $ istioctl authn tls-check istio-ingressgateway-db454d49b-lmtg8.istio-system httpbin.default.svc.cluster.local
  2. HOST:PORT                                  STATUS       SERVER     CLIENT     AUTHN POLICY     DESTINATION RULE
  3. 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.

Route rules have no effect on ingress gateway requests

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

  1. apiVersion: networking.istio.io/v1alpha3
  2. kind: VirtualService
  3. metadata:
  4.   name: myapp
  5. spec:
  6.   hosts:
  7.   - "myapp.com" # or maybe "*" if you are testing without DNS using the ingress-gateway IP (e.g., http://1.2.3.4/hello)
  8.   gateways:
  9.   - myapp-gateway
  10.   http:
  11.   - match:
  12.     - uri:
  13.         prefix: /hello
  14.     route:
  15.     - destination:
  16.         host: helloworld.default.svc.cluster.local
  17.   - match:
  18.     ...

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

  1. apiVersion: networking.istio.io/v1alpha3
  2. kind: VirtualService
  3. metadata:
  4.   name: helloworld
  5. spec:
  6.   hosts:
  7.   - helloworld.default.svc.cluster.local
  8.   http:
  9.   - route:
  10.     - destination:
  11.         host: helloworld.default.svc.cluster.local
  12.         subset: v1

In this situation you will notice that requests to the helloworld service via the ingress gateway willnot 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 of the helloworld service.Only internal requests with the host helloworld.default.svc.cluster.local will use thehelloworld VirtualService which directs traffic exclusively to subset v1.

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

  1. apiVersion: networking.istio.io/v1alpha3
  2. kind: VirtualService
  3. metadata:
  4.   name: myapp
  5. spec:
  6.   hosts:
  7.   - "myapp.com" # or maybe "*" if you are testing without DNS using the ingress-gateway IP (e.g., http://1.2.3.4/hello)
  8.   gateways:
  9.   - myapp-gateway
  10.   http:
  11.   - match:
  12.     - uri:
  13.         prefix: /hello
  14.     route:
  15.     - destination:
  16.         host: helloworld.default.svc.cluster.local
  17.         subset: v1
  18.   - match:
  19.     ...

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

  1. apiVersion: networking.istio.io/v1alpha3
  2. kind: VirtualService
  3. metadata:
  4.   name: myapp
  5. spec:
  6.   hosts:
  7.   - myapp.com # cannot use "*" here since this is being combined with the mesh services
  8.   - helloworld.default.svc.cluster.local
  9.   gateways:
  10.   - mesh # applies internally as well as externally
  11.   - myapp-gateway
  12.   http:
  13.   - match:
  14.     - uri:
  15.         prefix: /hello
  16.       gateways:
  17.       - myapp-gateway #restricts this rule to apply only to ingress gateway
  18.     route:
  19.     - destination:
  20.         host: helloworld.default.svc.cluster.local
  21.         subset: v1
  22.   - match:
  23.     - gateways:
  24.       - mesh # applies to all services inside the mesh
  25.     route:
  26.     - destination:
  27.         host: helloworld.default.svc.cluster.local
  28.         subset: v1

Headless TCP services losing connection

If istio-citadel is deployed, Envoy is restarted every 45 days 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 ofdisconnect, but if you still want to prevent the disconnects fromhappening, you will need to disable mutual TLS and the istio-citadel deployment.

First, edit your istio configuration to disable mutual TLS:

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

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

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

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

Envoy is crashing under load

Check your ulimit -a. Many systems have a 1024 open file descriptor limit by default which will cause Envoy to assert and crash with:

  1. [2017-05-17 03:00:52.735][14236][critical][assert] assert failure: fd_ != -1: external/envoy/source/common/network/connection_impl.cc:58

Make sure to raise your ulimit. Example: ulimit -n 16384

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, youwill 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:

  1. upstream http_backend {
  2.     server 127.0.0.1:8080;
  4.     keepalive 16;
  5. }
  7. server {
  8.     ...
  10.     location /http/ {
  11.         proxy_pass http://http_backend;
  12.         proxy_http_version 1.1;
  13.         proxy_set_header Connection "";
  14.         ...
  15.     }
  16. }

404 errors occur when multiple gateways configured with same TLS certificate

Configuring more than one gateway using the same TLS certificate will cause browsersthat leverage HTTP/2 connection reuse(i.e., most browsers) to produce 404 errors when accessing a second host after aconnection 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 gw2Since 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, itwill 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