istio.io/content/en/docs/ops/common-problems/network-issues/index.md

title	description	force_inline_toc	weight	aliases	owner	test
Traffic Management Problems	Techniques to address common Istio traffic management and network problems.	true	10	/help/ops/traffic-management/troubleshooting /help/ops/troubleshooting/network-issues /docs/ops/troubleshooting/network-issues	istio/wg-networking-maintainers	n/a

Requests are rejected by Envoy

Requests may be rejected for various reasons. The best way to understand why requests are being rejected is by 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:

{{< text bash >}} $ kubectl logs PODNAME -c istio-proxy -n NAMESPACE {{< /text >}}

In the default access log format, Envoy response flags are located after the response code, if you are using a custom log format, make sure to include %RESPONSE_FLAGS%.

Refer to the Envoy response flags for 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 a mutual TLS configuration conflict.

Route rules don't seem to affect traffic flow

With the current Envoy sidecar implementation, up to 100 requests may be required for weighted version 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 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.

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

503 errors after setting destination rule

{{< tip >}} You should only see this error if you disabled automatic mutual TLS during install. {{< /tip >}}

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 DestinationRule 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:

{{< text yaml >}} trafficPolicy: tls: mode: ISTIO_MUTUAL {{< /text >}}

Otherwise, the mode defaults to DISABLE 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.

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:

{{< text yaml >}} apiVersion: networking.istio.io/v1beta1 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: ... {{< /text >}}

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

{{< text yaml >}} apiVersion: networking.istio.io/v1beta1 kind: VirtualService metadata: name: helloworld spec: hosts:

• helloworld.default.svc.cluster.local http:
• route:
  • destination: host: helloworld.default.svc.cluster.local subset: v1 {{< /text >}}

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 of the helloworld service. Only 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 also include the subset rule in the myapp VirtualService:

{{< text yaml >}} apiVersion: networking.istio.io/v1beta1 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: ... {{< /text >}}

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

{{< text yaml >}} apiVersion: networking.istio.io/v1beta1 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 {{< /text >}}

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:

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

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, 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:

{{< text plain >}} 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 "";
    ...
}

} {{< /text >}}

503 error while accessing headless services

Assume Istio is installed with the following configuration:

• mTLS mode set to STRICT within the mesh
• meshConfig.outboundTrafficPolicy.mode set to ALLOW_ANY

Consider nginx is deployed as a StatefulSet in the default namespace and a corresponding Headless Service is defined as shown below:

{{< text yaml >}} apiVersion: v1 kind: Service metadata: name: nginx labels: app: nginx spec: ports:

• port: 80 name: http-web # Explicitly defining an http port clusterIP: None # Creates a Headless Service selector: app: nginx

---

apiVersion: apps/v1 kind: StatefulSet metadata: name: web spec: selector: matchLabels: app: nginx serviceName: "nginx" replicas: 3 template: metadata: labels: app: nginx spec: containers: - name: nginx image: registry.k8s.io/nginx-slim:0.8 ports: - containerPort: 80 name: web {{< /text >}}

The port name http-web in the Service definition explicitly specifies the http protocol for that port.

Let us assume we have a [sleep]({{< github_tree >}}/samples/sleep) pod Deployment as well in the default namespace. When nginx is accessed from this sleep pod using its Pod IP (this is one of the common ways to access a headless service), the request goes via the PassthroughCluster to the server-side, but the sidecar proxy on the server-side fails to find the route entry to nginx and fails with HTTP 503 UC.

{{< text bash >}} export SOURCE_POD=(kubectl get pod -l app=sleep -o jsonpath='{.items..metadata.name}') $ kubectl exec -it $SOURCE_POD -c sleep -- curl 10.1.1.171 -s -o /dev/null -w "%{http_code}" 503 {{< /text >}}

10.1.1.171 is the Pod IP of one of the replicas of nginx and the service is accessed on containerPort 80.

Here are some of the ways to avoid this 503 error:

1. Specify the correct Host header:

   The Host header in the curl request above will be the Pod IP by default. Specifying the Host header as nginx.default in our request to nginx successfully returns HTTP 200 OK.

   {{< text bash >}} export SOURCE_POD=(kubectl get pod -l app=sleep -o jsonpath='{.items..metadata.name}') $ kubectl exec -it $SOURCE_POD -c sleep -- curl -H "Host: nginx.default" 10.1.1.171 -s -o /dev/null -w "%{http_code}" 200 {{< /text >}}

2. Set port name to tcp or tcp-web or tcp-<custom_name>:

   Here the protocol is explicitly specified as tcp. In this case, only the TCP Proxy network filter on the sidecar proxy is used both on the client-side and server-side. HTTP Connection Manager is not used at all and therefore, any kind of header is not expected in the request.

   A request to nginx with or without explicitly setting the Host header successfully returns HTTP 200 OK.

   This is useful in certain scenarios where a client may not be able to include header information in the request.

   {{< text bash >}} export SOURCE_POD=(kubectl get pod -l app=sleep -o jsonpath='{.items..metadata.name}') $ kubectl exec -it $SOURCE_POD -c sleep -- curl 10.1.1.171 -s -o /dev/null -w "%{http_code}" 200 {{< /text >}}

   {{< text bash >}} $ kubectl exec -it $SOURCE_POD -c sleep -- curl -H "Host: nginx.default" 10.1.1.171 -s -o /dev/null -w "%{http_code}" 200 {{< /text >}}

3. Use domain name instead of Pod IP:

   A specific instance of a headless service can also be accessed using just the domain name.

   {{< text bash >}} export SOURCE_POD=(kubectl get pod -l app=sleep -o jsonpath='{.items..metadata.name}') $ kubectl exec -it $SOURCE_POD -c sleep -- curl web-0.nginx.default -s -o /dev/null -w "%{http_code}" 200 {{< /text >}}

   Here web-0 is the pod name of one of the 3 replicas of nginx.

Refer to this traffic routing page for some additional information on headless services and traffic routing behavior for different protocols.

TLS configuration mistakes

Many traffic management problems are caused by incorrect TLS configuration. The following sections describe some of the most common misconfigurations.

Sending HTTPS to an HTTP port

If your application sends an HTTPS request to a service declared to be HTTP, the Envoy sidecar will attempt to parse the request as HTTP while forwarding the request, which will fail because the HTTP is unexpectedly encrypted.

{{< text yaml >}} apiVersion: networking.istio.io/v1beta1 kind: ServiceEntry metadata: name: httpbin spec: hosts:

• httpbin.org ports:
• number: 443 name: http protocol: HTTP resolution: DNS {{< /text >}}

Although the above configuration may be correct if you are intentionally sending plaintext on port 443 (e.g., curl http://httpbin.org:443), generally port 443 is dedicated for HTTPS traffic.

Sending an HTTPS request like curl https://httpbin.org, which defaults to port 443, will result in an error like curl: (35) error:1408F10B:SSL routines:ssl3_get_record:wrong version number. The access logs may also show an error like 400 DPE.

To fix this, you should change the port protocol to HTTPS:

{{< text yaml >}} spec: ports:

• number: 443 name: https protocol: HTTPS {{< /text >}}

Gateway to virtual service TLS mismatch

There are two common TLS mismatches that can occur when binding a virtual service to a gateway.

1. The gateway terminates TLS while the virtual service configures TLS routing.
2. The gateway does TLS passthrough while the virtual service configures HTTP routing.

Gateway with TLS termination

{{< text yaml >}} apiVersion: networking.istio.io/v1beta1 kind: Gateway metadata: name: gateway namespace: istio-system spec: selector: istio: ingressgateway servers:

• port: number: 443 name: https protocol: HTTPS hosts:
  • "*" tls: mode: SIMPLE credentialName: sds-credential

---

apiVersion: networking.istio.io/v1beta1 kind: VirtualService metadata: name: httpbin spec: hosts:

• "*.example.com" gateways:
• istio-system/gateway tls:
• match:
  • sniHosts:
    • "*.example.com" route:
  • destination: host: httpbin.org {{< /text >}}

In this example, the gateway is terminating TLS (the tls.mode configuration of the gateway is SIMPLE, not PASSTHROUGH) while the virtual service is using TLS-based routing. Evaluating routing rules occurs after the gateway terminates TLS, so the TLS rule will have no effect because the request is then HTTP rather than HTTPS.

With this misconfiguration, you will end up getting 404 responses because the requests will be sent to HTTP routing but there are no HTTP routes configured. You can confirm this using the istioctl proxy-config routes command.

To fix this problem, you should switch the virtual service to specify http routing, instead of tls:

{{< text yaml >}} spec: ... http:

• match:
  • headers: ":authority": regex: "*.example.com" {{< /text >}}

Gateway with TLS passthrough

{{< text yaml >}} apiVersion: networking.istio.io/v1beta1 kind: Gateway metadata: name: gateway spec: selector: istio: ingressgateway servers:

• hosts:
  • "*" port: name: https number: 443 protocol: HTTPS tls: mode: PASSTHROUGH

---

apiVersion: networking.istio.io/v1beta1 kind: VirtualService metadata: name: virtual-service spec: gateways:

• gateway hosts:
• httpbin.example.com http:
• route:
  • destination: host: httpbin.org {{< /text >}}

In this configuration, the virtual service is attempting to match HTTP traffic against TLS traffic passed through the gateway. This will result in the virtual service configuration having no effect. You can observe that the HTTP route is not applied using the istioctl proxy-config listener and istioctl proxy-config route commands.

To fix this, you should switch the virtual service to configure tls routing:

{{< text yaml >}} spec: tls:

• match:
  • sniHosts: ["httpbin.example.com"] route:
  • destination: host: httpbin.org {{< /text >}}

Alternatively, you could terminate TLS, rather than passing it through, by switching the tls configuration in the gateway:

{{< text yaml >}} spec: ... tls: credentialName: sds-credential mode: SIMPLE {{< /text >}}

Double TLS (TLS origination for a TLS request)

When configuring Istio to perform {{< gloss >}}TLS origination{{< /gloss >}}, you need to make sure that the application sends plaintext requests to the sidecar, which will then originate the TLS.

The following DestinationRule originates TLS for requests to the httpbin.org service, but the corresponding ServiceEntry defines the protocol as HTTPS on port 443.

{{< text yaml >}} apiVersion: networking.istio.io/v1beta1 kind: ServiceEntry metadata: name: httpbin spec: hosts:

• httpbin.org ports:
• number: 443 name: https protocol: HTTPS resolution: DNS

---

apiVersion: networking.istio.io/v1beta1 kind: DestinationRule metadata: name: originate-tls spec: host: httpbin.org trafficPolicy: tls: mode: SIMPLE {{< /text >}}

With this configuration, the sidecar expects the application to send TLS traffic on port 443 (e.g., curl https://httpbin.org), but it will also perform TLS origination before forwarding requests. This will cause the requests to be double encrypted.

For example, sending a request like curl https://httpbin.org will result in an error: (35) error:1408F10B:SSL routines:ssl3_get_record:wrong version number.

You can fix this example by changing the port protocol in the ServiceEntry to HTTP:

{{< text yaml >}} spec: hosts:

• httpbin.org ports:
• number: 443 name: http protocol: HTTP {{< /text >}}

Note that with this configuration your application will need to send plaintext requests to port 443, like curl http://httpbin.org:443, because TLS origination does not change the port. However, starting in Istio 1.8, you can expose HTTP port 80 to the application (e.g., curl http://httpbin.org) and then redirect requests to targetPort 443 for the TLS origination:

{{< text yaml >}} spec: hosts:

• httpbin.org ports:
• number: 80 name: http protocol: HTTP targetPort: 443 {{< /text >}}

404 errors occur 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

Configuring SNI routing when not sending SNI

An HTTPS Gateway that specifies the hosts field will perform an SNI match on incoming requests. For example, the following configuration would only allow requests that match *.example.com in the SNI:

{{< text yaml >}} servers:

• port: number: 443 name: https protocol: HTTPS hosts:
  • "*.example.com" {{< /text >}}

This may cause certain requests to fail.

For example, if you do not have DNS set up and are instead directly setting the host header, such as curl 1.2.3.4 -H "Host: app.example.com", no SNI will be set, causing the request to fail. Instead, you can set up DNS or use the --resolve flag of curl. See the Secure Gateways task for more information.

Another common issue is load balancers in front of Istio. Most cloud load balancers will not forward the SNI, so if you are terminating TLS in your cloud load balancer you may need to do one of the following:

• Configure the cloud load balancer to instead passthrough the TLS connection
• Disable SNI matching in the Gateway by setting the hosts field to *

A common symptom of this is for the load balancer health checks to succeed while real traffic fails.

Unchanged Envoy filter configuration suddenly stops working

An EnvoyFilter configuration that specifies an insert position relative to another filter can be very fragile because, by default, the order of evaluation is based on the creation time of the filters. Consider a filter with the following specification:

{{< text yaml >}} spec: configPatches:

• applyTo: NETWORK_FILTER match: context: SIDECAR_OUTBOUND listener: portNumber: 443 filterChain: filter: name: istio.stats patch: operation: INSERT_BEFORE value: ... {{< /text >}}

To work properly, this filter configuration depends on the istio.stats filter having an older creation time than it. Otherwise, the INSERT_BEFORE operation will be silently ignored. There will be nothing in the error log to indicate that this filter has not been added to the chain.

This is particularly problematic when matching filters, like istio.stats, that are version specific (i.e., that include the proxyVersion field in their match criteria). Such filters may be removed or replaced by newer ones when upgrading Istio. As a result, an EnvoyFilter like the one above may initially be working perfectly but after upgrading Istio to a newer version it will no longer be included in the network filter chain of the sidecars.

To avoid this issue, you can either change the operation to one that does not depend on the presence of another filter (e.g., INSERT_FIRST), or set an explicit priority in the EnvoyFilter to override the default creation time-based ordering. For example, adding priority: 10 to the above filter will ensure that it is processed after the istio.stats filter which has a default priority of 0.

Virtual service with fault injection and retry/timeout policies not working as expected

Currently, Istio does not support configuring fault injections and retry or timeout policies on the same VirtualService. Consider the following configuration:

{{< text yaml >}} apiVersion: networking.istio.io/v1alpha3 kind: VirtualService metadata: name: helloworld spec: hosts: - "*" gateways:

• helloworld-gateway http:
• match:
  • uri: exact: /hello fault: abort: httpStatus: 500 percentage: value: 50 retries: attempts: 5 retryOn: 5xx route:
  • destination: host: helloworld port: number: 5000 {{< /text >}}

You would expect that given the configured five retry attempts, the user would almost never see any errors when calling the helloworld service. However since both fault and retries are configured on the same VirtualService, the retry configuration does not take effect, resulting in a 50% failure rate. To work around this issue, you may remove the fault config from your VirtualService and inject the fault to the upstream Envoy proxy using EnvoyFilter instead:

{{< text yaml >}} apiVersion: networking.istio.io/v1alpha3 kind: EnvoyFilter metadata: name: hello-world-filter spec: workloadSelector: labels: app: helloworld configPatches:

• applyTo: HTTP_FILTER match: context: SIDECAR_INBOUND # will match outbound listeners in all sidecars listener: filterChain: filter: name: "envoy.filters.network.http_connection_manager" patch: operation: INSERT_BEFORE value: name: envoy.fault typed_config: "@type": "type.googleapis.com/envoy.extensions.filters.http.fault.v3.HTTPFault" abort: http_status: 500 percentage: numerator: 50 denominator: HUNDRED {{< /text >}}

This works because this way the retry policy is configured for the client proxy while the fault injection is configured for the upstream proxy.