Explicit Deny

4 minute read page test

This task shows you how to set up Istio authorization policy of DENY action to explicitly deny traffic in an Istio mesh. This is different from the ALLOW action because the DENY action has higher priority and will not be bypassed by any ALLOW actions.

Before you begin

Before you begin this task, do the following:

Read the Istio authorization concepts.
Follow the Istio installation guide to install Istio.
Deploy workloads:
This task uses two workloads, httpbin and curl, deployed on one namespace, foo. Both workloads run with an Envoy proxy in front of each. Deploy the example namespace and workloads with the following command:
ZipZip
```
$ kubectl create ns foo
$ kubectl apply -f <(istioctl kube-inject -f @samples/httpbin/httpbin.yaml@) -n foo
$ kubectl apply -f <(istioctl kube-inject -f @samples/curl/curl.yaml@) -n foo
```

Verify that curl talks to httpbin with the following command:

$ kubectl exec "$(kubectl get pod -l app=curl -n foo -o jsonpath={.items..metadata.name})" -c curl -n foo -- curl http://httpbin.foo:8000/ip -sS -o /dev/null -w "%{http_code}\n"
200

Explicitly deny a request

The following command creates the deny-method-get authorization policy for the httpbin workload in the foo namespace. The policy sets the action to DENY to deny requests that satisfy the conditions set in the rules section. This type of policy is better known as a deny policy. In this case, the policy denies requests if their method is GET.
```
$ kubectl apply -f - <<EOF
apiVersion: security.istio.io/v1
kind: AuthorizationPolicy
metadata:
  name: deny-method-get
  namespace: foo
spec:
  selector:
    matchLabels:
      app: httpbin
  action: DENY
  rules:
  - to:
    - operation:
        methods: ["GET"]
EOF
```

Verify that GET requests are denied:

$ kubectl exec "$(kubectl get pod -l app=curl -n foo -o jsonpath={.items..metadata.name})" -c curl -n foo -- curl "http://httpbin.foo:8000/get" -X GET -sS -o /dev/null -w "%{http_code}\n"
403

Verify that POST requests are allowed:

$ kubectl exec "$(kubectl get pod -l app=curl -n foo -o jsonpath={.items..metadata.name})" -c curl -n foo -- curl "http://httpbin.foo:8000/post" -X POST -sS -o /dev/null -w "%{http_code}\n"
200

Update the deny-method-get authorization policy to deny GET requests only if the x-token value of the HTTP header is not admin. The following example policy sets the value of the notValues field to ["admin"] to deny requests with a header value that is not admin:

$ kubectl apply -f - <<EOF
apiVersion: security.istio.io/v1
kind: AuthorizationPolicy
metadata:
  name: deny-method-get
  namespace: foo
spec:
  selector:
    matchLabels:
      app: httpbin
  action: DENY
  rules:
  - to:
    - operation:
        methods: ["GET"]
    when:
    - key: request.headers[x-token]
      notValues: ["admin"]
EOF

Verify that GET requests with the HTTP header x-token: admin are allowed:

$ kubectl exec "$(kubectl get pod -l app=curl -n foo -o jsonpath={.items..metadata.name})" -c curl -n foo -- curl "http://httpbin.foo:8000/get" -X GET -H "x-token: admin" -sS -o /dev/null -w "%{http_code}\n"
200

Verify that GET requests with the HTTP header x-token: guest are denied:

$ kubectl exec "$(kubectl get pod -l app=curl -n foo -o jsonpath={.items..metadata.name})" -c curl -n foo -- curl "http://httpbin.foo:8000/get" -X GET -H "x-token: guest" -sS -o /dev/null -w "%{http_code}\n"
403

The following command creates the allow-path-ip authorization policy to allow requests at the /ip path to the httpbin workload. This authorization policy sets the action field to ALLOW. This type of policy is better known as an allow policy.

$ kubectl apply -f - <<EOF
apiVersion: security.istio.io/v1
kind: AuthorizationPolicy
metadata:
  name: allow-path-ip
  namespace: foo
spec:
  selector:
    matchLabels:
      app: httpbin
  action: ALLOW
  rules:
  - to:
    - operation:
        paths: ["/ip"]
EOF

Verify that GET requests with the HTTP header x-token: guest at path /ip are denied by the deny-method-get policy. Deny policies takes precedence over the allow policies:

$ kubectl exec "$(kubectl get pod -l app=curl -n foo -o jsonpath={.items..metadata.name})" -c curl -n foo -- curl "http://httpbin.foo:8000/ip" -X GET -H "x-token: guest" -s -o /dev/null -w "%{http_code}\n"
403

Verify that GET requests with the HTTP header x-token: admin at path /ip are allowed by the allow-path-ip policy:

$ kubectl exec "$(kubectl get pod -l app=curl -n foo -o jsonpath={.items..metadata.name})" -c curl -n foo -- curl "http://httpbin.foo:8000/ip" -X GET -H "x-token: admin" -s -o /dev/null -w "%{http_code}\n"
200

Verify that GET requests with the HTTP header x-token: admin at path /get are denied because they don’t match the allow-path-ip policy:

$ kubectl exec "$(kubectl get pod -l app=curl -n foo -o jsonpath={.items..metadata.name})" -c curl -n foo -- curl "http://httpbin.foo:8000/get" -X GET -H "x-token: admin" -s -o /dev/null -w "%{http_code}\n"
403

Clean up

Remove the namespace foo from your configuration:

$ kubectl delete namespace foo