Skipper is an HTTP router and reverse proxy for service composition. It's designed to handle >100k HTTP route definitions with detailed lookup conditions, and flexible augmentation of the request flow with filters. It can be used out of the box or extended with custom lookup, filter logic and configuration sources.

The Skoap filters can be found currently in the branch called 'skoap-migration'. The original incubator repository at zalando-incubator/skoap has been removed.

An overview of deployments and data-clients shows some use cases to run skipper.

Skipper

• identifies routes based on the requests' properties, such as path, method, host and headers
• allows modification of the requests and responses with filters that are independently configured for each route
• simultaneously streams incoming requests and backend responses
• optionally acts as a final endpoint (shunt), e.g. as a static file server or a mock backend for diagnostics
• updates routing rules without downtime, while supporting multiple types of data sources — including etcd, Kubernetes Ingress, Innkeeper, static files, route string and custom configuration sources
• can serve as a Kubernetes Ingress controller without reloads. You can use it in combination with a controller that will route public traffic to your skipper fleet; see AWS example
• shipped with eskip: a descriptive configuration language designed for routing rules

Skipper provides a default executable command with a few built-in filters. However, its primary use case is to be extended with custom filters, predicates or data sources. Go here for additional documentation.

A few examples for extending Skipper:

• Authentication proxy https://github.com/zalando-incubator/skoap (repository removed see 'skoap-migration' branch)
• Image server https://github.com/zalando-stups/skrop
• Plugins https://github.com/skipper-plugins/

In order to build and run Skipper, only the latest version of Go needs to be installed. Skipper can use Innkeeper or Etcd as data sources for routes, or for the simplest cases, a local configuration file. See more details in the documentation: https://godoc.org/github.com/zalando/skipper.

Skipper is 'go get' compatible. If needed, create a Go workspace first:

mkdir ws
cd ws
export GOPATH=$(pwd)
export PATH=$PATH:$GOPATH/bin

Get the Skipper packages:

go get github.com/zalando/skipper/...

Create a file with a route:

echo 'hello: Path("/hello") -> "https://www.example.org"' > example.eskip

Optionally, verify the file's syntax:

eskip check example.eskip

Start Skipper and make an HTTP request:

skipper -routes-file example.eskip &
curl localhost:9090/hello

To run the latest Docker container:

docker run registry.opensource.zalan.do/pathfinder/skipper:latest

Getting the code with the test dependencies (-t switch):

go get -t github.com/zalando/skipper/...

Build and test all packages:

cd src/github.com/zalando/skipper
make deps
make install
make check

Skipper can be used to run as an Kubernetes Ingress controller. Details with examples of Skipper's capabilities and an overview you will can be found in our deployment docs.

For AWS integration, we provide an ingress controller https://github.com/zalando-incubator/kube-ingress-aws-controller, that manage ALBs in front of your skipper deployment. A production example, https://github.com/zalando-incubator/kubernetes-on-aws/blob/dev/cluster/manifests/skipper/daemonset.yaml, can be found in our Kubernetes configuration https://github.com/zalando-incubator/kubernetes-on-aws.

Skipper's Documentation and Godoc developer documentation, includes information about deployment use cases and detailed information on these topics:

• The Routing Mechanism
• Matching Requests
• Filters - Augmenting Requests and Responses
• Service Backends
• Route Definitions
• Data Sources: eskip file, etcd, Inkeeper API, Kubernetes, Route string
• Circuit Breakers
• Extending It with Customized Predicates, Filters, and Builds
• Predicates - additional predicates to match a route
• Proxy Packages
• Logging and Metrics
• Performance Considerations
• Rate Limiters
• Opentracing plugin

The following example shows a skipper routes file in eskip format, that has 3 named routes: baidu, google and yandex.

% cat doc-1min-intro.eskip
baidu:
        Path("/baidu")
        -> setRequestHeader("Host", "www.baidu.com")
        -> setPath("/s")
        -> setQuery("wd", "godoc skipper")
        -> "http://www.baidu.com";
google:
        *
        -> setPath("/search")
        -> setQuery("q", "godoc skipper")
        -> "https://www.google.com";
yandex:
        * && Cookie("yandex", "true")
        -> setPath("/search/")
        -> setQuery("text", "godoc skipper")
        -> tee("http://127.0.0.1:12345/")
        -> "https://yandex.ru";

Matching the route:

• baidu is using Path() matching to differentiate the HTTP requests to select the route.
• google is the default matching with wildcard '*'
• yandex is the default matching with wildcard '*' if you have a cookie "yandex=true"

Request Filters:

• If baidu is selected, skipper sets the Host header, changes the path and sets a query string to the http request to the backend "http://www.baidu.com".
• If google is selected, skipper changes the path and sets a query string to the http request to the backend "https://www.google.com".
• If yandex is selected, skipper changes the path and sets a query string to the http request to the backend "https://yandex.ru". The modified request will be copied to "http://127.0.0.1:12345/"

Run skipper with the routes file doc-1min-intro.eskip shown above

% skipper -routes-file doc-1min-intro.eskip

To test each route you can use curl:

% curl -v localhost:9090/baidu
% curl -v localhost:9090/
% curl -v --cookie "yandex=true" localhost:9090/

To see the request that is made by the tee() filter you can use nc:

[terminal1]% nc -l 12345
[terminal2]% curl -v --cookie "yandex=true" localhost:9090/

You should have a base understanding of Kubernetes and Ingress.

Prerequisites: First you have to install skipper-ingress as for example daemonset, create a deployment and a service.

We start to deploy skipper-ingress as a daemonset, use hostNetwork and expose the TCP port 9999 on each Kubernetes worker node for incoming ingress traffic.

% cat skipper-ingress-ds.yaml
apiVersion: extensions/v1beta1
kind: DaemonSet
metadata:
  name: skipper-ingress
  namespace: kube-system
  labels:
    application: skipper-ingress
    version: v0.9.115
    component: ingress
spec:
  selector:
    matchLabels:
      application: skipper-ingress
  updateStrategy:
    type: RollingUpdate
  template:
    metadata:
      name: skipper-ingress
      labels:
        application: skipper-ingress
        version: v0.9.115
        component: ingress
      annotations:
        scheduler.alpha.kubernetes.io/critical-pod: ''
    spec:
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
            - matchExpressions:
              - key: master
                operator: DoesNotExist
      tolerations:
      - key: CriticalAddonsOnly
        operator: Exists
      hostNetwork: true
      containers:
      - name: skipper-ingress
        image: registry.opensource.zalan.do/pathfinder/skipper:v0.9.115
        ports:
        - name: ingress-port
          containerPort: 9999
          hostPort: 9999
        args:
          - "skipper"
          - "-kubernetes"
          - "-kubernetes-in-cluster"
          - "-address=:9999"
          - "-proxy-preserve-host"
          - "-serve-host-metrics"
          - "-enable-ratelimits"
          - "-experimental-upgrade"
          - "-metrics-exp-decay-sample"
        resources:
          limits:
            cpu: 200m
            memory: 200Mi
          requests:
            cpu: 25m
            memory: 25Mi
        readinessProbe:
          httpGet:
            path: /kube-system/healthz
            port: 9999
          initialDelaySeconds: 5
          timeoutSeconds: 5

We now deploy a simple demo application serving html:

% cat demo-deployment.yaml
apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: skipper-demo
spec:
  replicas: 2
  template:
    metadata:
      labels:
        application: skipper-demo
    spec:
      containers:
      - name: skipper-demo
        image: registry.opensource.zalan.do/pathfinder/skipper:v0.9.117
        args:
          - "skipper"
          - "-inline-routes"
          - "* -> inlineContent(\"<body style='color: white; background-color: green;'><h1>Hello!</h1>\") -> <shunt>"
        ports:
        - containerPort: 9090

We deploy a service type ClusterIP that we will select from ingress:

% cat demo-svc.yaml
apiVersion: v1
kind: Service
metadata:
  name: sszuecs-demo
  labels:
    application: skipper-demo
spec:
  type: ClusterIP
  ports:
    - port: 80
      protocol: TCP
      targetPort: 9090
      name: external
  selector:
    application: sszuecs-demo

To deploy both, you have to run:

% kubectl create -f demo-deployment.yaml
% kubectl create -f demo-svc.yaml

Now we have a skipper-ingress running as daemonset exposing the TCP port 9999 on each worker node, a backend application running with 2 replicas that serves some html on TCP port 9090, and we expose a cluster service on TCP port 80. Besides skipper-ingress, deployment and service can not be reached from outside the cluster. Now we expose the application with Ingress to the external network:

% cat demo-ing.yaml
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: skipper-demo
spec:
  rules:
  - host: skipper-demo.<mydomain.org>
    http:
      paths:
      - backend:
          serviceName: skipper-demo
          servicePort: 80

To deploy this ingress, you have to run:

% kubectl create -f demo-ing.yaml

Skipper will configure itself for the given ingress, such that you can test doing:

% curl -v -H"Host: skipper-demo.<mydomain.org>" http://<nodeip>:9999/

The next question you may ask is: how to expose this to your customers?

The answer depends on your setup and complexity requirements. In the simplest case you could add one A record in your DNS *.<mydomain.org> to your frontend loadbalancer IP that directs all traffic from *.<mydomain.org> to all Kubernetes worker nodes on TCP port 9999.

A more complex setup we use in production and can be done with something that configures your frontend loadbalancer, for example kube-aws-ingress-controller, and your DNS, external-dns automatically.

See https://github.com/zalando/skipper/blob/master/packaging/readme.md

In case you want to implement and link your own modules into your skipper for more advanced features like opentracing API support there is https://github.com/skipper-plugins organization to enable you to do so. In order to explain you the build process with custom Go modules there is https://github.com/skipper-plugins/skipper-tracing-build, that is used to build skipper's opentracing package.

User or developer questions can be asked in our public Google Group

We do our proposals open in Skipper's Google drive. If you want to make a proposal feel free to create an issue and if it is a bigger change we will invite you to a document, such that we can work together.