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Kubernetes/Ingress

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< Kubernetes
Revision as of 22:42, 24 February 2022 by imported>JMeybohm
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Introduction

The Kubernetes Ingress uses Istio Ingresscontroller (ultimately the Ingressgateway) running as a Daemonset on each worker node to route traffic to workload services and (in last instance) Pods.

The Istio Ingressgateway is implemented as an envoy instance that is configured via xDS by the Istiod Control Plane. All configuration is derived from Kubernetes API Objects like the Service Objects as well as Istio specific custom resources: Gateway, VirtualService and DestinationRule.

The process of configuring the Ingressgateway is abstracted away from service owners/deployers via helm common_templates/0.4/_ingress_helpers.tpl so that it is enough to specify .Values.ingress.enabled: true for a very basic setup.

  • ingressgateway terminates TLS connections from clients
  • ingressgateway establishes TLS connections to upstream (pods) which will be terminated on pod level by service-proxy

Setup and configuration

Istio (the control plane as well as components like the Ingressgateway) are installed and initially configured using istioctl (from a deployment host) together with an environment specific config in custom_deploy.d/istio.

For initial installation or deploying updates, run (on a deployment host):

istioctl-1.9.5 apply -f <environment>/config.yaml

For details on how to configure Istio, please see:

Some parts of the configuration have to be (or can be) done via helm chart values. istioctl comes with embedded helm charts that get rendered and applied by istiotcl directly. You may find those embedded charts (to look up possible configuration options etc. at:

TLS certificates are generated and maintained by cert-manager and deployed into the istio-system namespace for the ingressgateway to pick them up. This is configured and deployed by SRE via helmfile.d/admin_ng/helmfile_namespace_certs.yaml ??. If a service needs to be made available under additional hostnames they need to be configured at as tlsHostname in the namespaces config (helmfile.d/admin_ng/values/*.yaml).

Troubleshooting

The Ingressgateway does emit access logs which can be viewed in logstash

Generic grafana dashboards can be found via the istio tag: Grafana search

Status of the ingressgateway

Using 'proxy-status' it can be checked if the istio control-plane is successfully sending updates to the ingressgateway instances:

istioctl-1.9.5 proxy-status

Retrieve clusters, listeners, routes, endpoints, secrets

istioctl can be used to fetch specific parts of the (envoy) configuration.

Be aware that ingressgateway will show a cluster and endpoint for every kubernetes service in the cluster, regardless of whether you have configured ingress for it or not (it's just discovering everything in the cluster).

# <COMPONENT> can be one of: clusters, endpoints, listeners, routes, secrets
istioctl-1.9.5 -n istio-system proxy-config <COMPONENT> daemonset/istio-ingressgateway

# You can output as JSON (-o json) for a huge amount of detail.

When needing to troubleshoot TLS certificates used, the JSON output can be parsed with jq and piped into openssl, e.g:

# <RESOURCE NAME> is the name of the certificate as returned by:
istioctl-1.9.5 -n istio-system proxy-config secrets daemonset/istio-ingressgateway

# Dump a certificate chain
istioctl-1.9.5 -n istio-system proxy-config secrets daemonset/istio-ingressgateway -o json | \
  jq '[.dynamicActiveSecrets[] | select(.name == "<RESOURCE NAME>")][0].secret.tlsCertificate.certificateChain.inlineBytes' -r | \
  base64 -d | \
  openssl crl2pkcs7 -nocrl -certfile /dev/stdin | openssl pkcs7 -print_certs -text -noout

# Dump a CA
istioctl-1.9.5 -n istio-system proxy-config secrets daemonset/istio-ingressgateway -o json | \
  jq '[.dynamicActiveSecrets[] | select(.name == "<RESOURCE NAME>")][0].secret.validationContext.trustedCa.inlineBytes' -r | \
  base64 -d | \
  openssl crl2pkcs7 -nocrl -certfile /dev/stdin | openssl pkcs7 -print_certs -text -noout

Dump complete envoy config

If needed, the complete (currently active) envoy config can be dumped from the ingressgateway:

kubectl -n istio-system exec -it daemonset/istio-ingressgateway -- \
  /bin/bash -c 'exec 5<>/dev/tcp/127.0.0.1/15000; echo -ne "GET /config_dump HTTP/1.1\r\nHost: localhost:15000\r\nConnection: close\r\n\r\n" >&5; cat <&5'

See https://www.envoyproxy.io/docs/envoy/latest/operations/admin.html for details on interacting with the envoy admin interface.

You can always kubectl -n istio-system port-forward daemonset/istio-ingressgateway 15000:15000 if you need to deal with it more.

Enable debug logging

Envoy component logging can be changed via istioctl as well:

# Print all components and the currently configured log level:
istioctl-1.9.5 -n istio-system proxy-config log daemonset/istio-ingressgateway

# Change to level of a specific component (admin in this case) to info
istioctl-1.9.5 -n istio-system proxy-config log daemonset/istio-ingressgateway --level admin:info

# Change the levels of all components to info
istioctl-1.9.5 -n istio-system proxy-config log daemonset/istio-ingressgateway --level info


Configuration (for service owners)

To enable Ingress for your chart you need to undertake the following steps:

For the absolute basic setup, all you need to do not is enable ingress via your values.yaml:

ingress:
  enabled: true
  staging: true # If you are doing this for a staging service

This will make your service available as https://SERVICE_NAME.discovery.wmnet (https://SERVICE_NAME.staging.discovery.wmnet for staging) traffic will be routed as is to all pods of your service in a round-robin fashion.

You may configure more complex routing logic, listen to different or more than one hostname etc. via the ingress configuration stanza. Please keep in mind that for different or additional hostnames you may need SRE assistance to set up certificates etc.

The routing behavior may be modified via the ingress.httproutes stanza which supports all options described in https://istio.io/v1.9/docs/reference/config/networking/virtual-service/#HTTPRoute.

If you want to make several services available as subpaths of a hostname (https://SERVICE_NAME.discovery.wmnet/foo, https://SERVICE_NAME.discovery.wmnet/bar, ...) you need to make sure to configure only one Istio Gateway (in one of your helm chart releases) for this hostname and attach multiple HTTPRoute objects to it. Multiple Istio Gateway objects claiming the same hostname will simply be ignored.

Assuming you have two releases of your chart (one and two), you may configure ingress like in the following example to achieve that:

---
# release "one" values.yaml:
# made available as https://SERVICE_NAME.discovery.wmnet/one
# via default options + httproute
ingress:
  enabled: true
  httproutes:
  - match:
    - uri:
        prefix: /one
---
# release "two" values.yaml:
# made available as https://SERVICE_NAME.discovery.wmnet/two
# via the Gateway deployed by release "one"
ingress:
  enabled: true
  existingGateway: "SERVICE_NAMESPACE/one" # referencing the Gateway deployed by the release "one"
  routeHosts:
  - SERVICE_NAME.discovery.wmnet # Attach the following routes to this hostname in the referenced Gateway
  httproutes:
  - match:
    - uri:
        prefix: /two
    route:
    - destination:
      host: two-tls-service.SERVICE_NAMESPACE.svc.cluster.local # The cluster internal DNS name for this releases service
      port:
        number: SERVICE_TLS_PUBLIC_PORT # Port you defined in .Values.tls.public_port