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Mutual TLS (mTLS)

Mutual TLS (mTLS)

In this guide, you learn how to set up an mTLS Gateway. Before the client application and the Gateway establish a connection, both parties must exchange certificates to verify their identities. After a TLS connection is established, the TLS connection is terminated at the Gateway and the unencrypted HTTP traffic is forwarded to the backend destination.

Before you begin

  1. Set up kgateway by following the Quick start or Installation guides.

  2. Deploy the httpbin sample app.

  3. Make sure that you have the OpenSSL version of openssl, not LibreSSL. The openssl version must be at least 1.1.

    1. Check the openssl version that is installed. If you see LibreSSL in the output, continue to the next step.

      openssl version

    2. Install the OpenSSL version (not LibreSSL). For example, you might use Homebrew.

      brew install openssl

    3. Review the output of the OpenSSL installation for the path of the binary file. You can choose to export the binary to your path, or call the entire path whenever the following steps use an openssl command.

      • For example, openssl might be installed along the following path: /usr/local/opt/openssl@3/bin/
      • To run commands, you can append the path so that your terminal uses this installed version of OpenSSL, and not the default LibreSSL. /usr/local/opt/openssl@3/bin/openssl req -new -newkey rsa:4096 -x509 -sha256 -days 3650...
  4. Decide whether to set up a listener inline on the Gateway resource or as a separate ListenerSet resource. For more information, see the Listener overview.

    ListenerSets: This feature is available in kgateway version 2.1.x or later. Also, you must install the experimental channel of the Kubernetes Gateway API at version 1.3 or later.

Create self-signed TLS certificates

Create self-signed TLS certificates that you use for the mutual TLS connection between your client application (curl) and the gateway proxy.

⚠️
Self-signed certificates are used for demonstration purposes. Do not use self-signed certificates in production environments. Instead, use certificates that are issued from a trust Certificate Authority.

  1. Create a root certificate for the example.com domain. You use this certificate to sign the certificate for your client and gateway later.

    mkdir example_certs
openssl req -x509 -sha256 -nodes -days 365 -newkey rsa:2048 -subj '/O=example Inc./CN=example.com' -keyout example_certs/example.com.key -out example_certs/example.com.crt

  2. Create a gateway certificate that is signed by the root CA certificate that you created in the previous step.

    openssl req -out example_certs/gateway.csr -newkey rsa:2048 -nodes -keyout example_certs/gateway.key -subj "/CN=*/O=any domain"
openssl x509 -req -sha256 -days 365 -CA example_certs/example.com.crt -CAkey example_certs/example.com.key -set_serial 0 -in example_certs/gateway.csr -out example_certs/gateway.crt

  3. Create a Kubernetes secret to store your gateway TLS certificate. You create the secret in the same cluster and namespace that the gateway is deployed to. By including a rootca certificate, Gloo Gateway is automatically configured for mutual TLS with the downstream application.

    export TLS_CERT="$(< example_certs/gateway.crt)"  
export TLS_KEY="$(< example_certs/gateway.key)"  
export CA_CERT="$(< example_certs/example.com.crt)"

cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Secret
metadata:
  name: https
  namespace: kgateway-system
  labels: 
    gateway: https
type: kubernetes.io/tls
stringData:
  tls.crt: |
$(echo "$TLS_CERT" | sed 's/^/    /')
  tls.key: |
$(echo "$TLS_KEY" | sed 's/^/    /')
  ca.crt: | 
$(echo "$CA_CERT" | sed 's/^/    /')
EOF

  4. Create a client certificate and private key. You use these credentials later when sending a request to the gateway proxy. The client certificate is signed with the same root CA certificate that you used for the gateway proxy.

    openssl req -out example_certs/client.example.com.csr -newkey rsa:2048 -nodes -keyout example_certs/client.example.com.key -subj "/CN=client.example.com/O=client organization"
openssl x509 -req -sha256 -days 365 -CA example_certs/example.com.crt -CAkey example_certs/example.com.key -set_serial 1 -in example_certs/client.example.com.csr -out example_certs/client.example.com.crt

Set up an mTLS listener

  1. Create a mTLS Gateway that is configured with the TLS certificates that you set up earlier. To use the default Envoy-based kgateway proxy, set the gatewayClassName to kgateway. To use agentgateway, set the gatewayClassName to agentgateway.

    kubectl apply -f- <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  name: https
  namespace: kgateway-system
  labels:
    gateway: https
spec:
  gatewayClassName: kgateway
  listeners:
    - name: https
      port: 443
      protocol: HTTPS
      hostname: https.example.com
      tls:
        mode: Terminate
        certificateRefs:
          - name: https
            kind: Secret
      allowedRoutes:
        namespaces:
          from: All
EOF
    Setting Description
    spec.gatewayClassName The name of the Kubernetes gateway class that you want to use to configure the gateway.
    spec.listeners Configure the listeners for this gateway. In this example, you configure an HTTPS gateway that listens for incoming traffic on port 443.
    spec.listeners.tls.mode The TLS mode that you want to use for incoming requests. In this example, HTTPS requests are terminated at the gateway and the unencrypted request is forwarded to the service in the cluster.
    spec.listeners.tls.certificateRefs The Kubernetes secret that holds the TLS certificate and key for the gateway. The gateway uses these credentials to establish the TLS connection with a client, and to decrypt incoming HTTPS requests.

    1. Create a Gateway that enables the attachment of ListenerSets.

      kubectl apply -f- <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  name: https
  namespace: kgateway-system
  labels:
    gateway: https
spec:
  gatewayClassName: kgateway
  allowedListeners:
    namespaces:
      from: All
  listeners:
  - protocol: HTTP
    port: 80
    name: http
    allowedRoutes:
      namespaces:
        from: All     
EOF
      Setting Description
      spec.gatewayClassName The name of the Kubernetes gateway class that you want to use to configure the gateway.
      spec.allowedListeners Enable the attachment of ListenerSets to this Gateway. The example allows listeners from any namespace, which is helpful in multitenant environments. You can also limit the allowed listeners. To limit to listeners in the same namespace as the Gateway, set this value to Same. To limit to listeners with a particular label, set this value to Selector.
      spec.listeners Optionally, you can configure a listener that is specific to the Gateway. Note that due to a Gateway API limitation, you must configure at least one listener on the Gateway resource, even if the listener is not used and is a “dummy” listener. This dummy listener cannot conflict with the listener that you configure in the ListenerSet, such as using the same port or name. In this example, the dummy listener is configured on HTTP port 80, which differs from HTTPS port 443 in the ListenerSet that you create later.

    2. Create a ListenerSet that configures an HTTPS listener for the Gateway.

      kubectl apply -f- <<EOF
apiVersion: gateway.networking.x-k8s.io/v1alpha1
kind: XListenerSet
metadata:
  name: https-listenerset
  namespace: kgateway-system
  labels:
    gateway: https
spec:
  parentRef:
    name: https
    namespace: kgateway-system
    kind: Gateway
    group: gateway.networking.k8s.io
  listeners:
  - name: https
    port: 443
    protocol: HTTPS
    hostname: https.example.com
    tls:
      mode: Terminate
      certificateRefs:
        - name: https
          kind: Secret
    allowedRoutes:
      namespaces:
        from: All
EOF
      Setting Description
      spec.parentRef The name of the Gateway to attach the ListenerSet to.
      spec.listeners Configure the listeners for this gateway. In this example, you configure an HTTPS gateway that listens for incoming traffic on port 443.
      spec.listeners.tls.mode The TLS mode that you want to use for incoming requests. In this example, HTTPS requests are terminated at the gateway and the unencrypted request is forwarded to the service in the cluster.
      spec.listeners.tls.certificateRefs The Kubernetes secret that holds the TLS certificate and key for the gateway. The gateway uses these credentials to establish the TLS connection with a client, and to decrypt incoming HTTPS requests.

  2. Create an HTTPRoute for the httpbin app and add it to the HTTPS gateway that you created.

    kubectl apply -f- <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: httpbin-https
  namespace: httpbin
  labels:
    example: httpbin-route
    gateway: https
spec:
  parentRefs:
    - name: https
      namespace: kgateway-system
  rules:
    - backendRefs:
        - name: httpbin
          port: 8000
EOF
    kubectl apply -f- <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: httpbin-https
  namespace: httpbin
  labels:
    example: httpbin-route
    gateway: https
spec:
  parentRefs:
    - name: https-listenerset
      namespace: kgateway-system
      kind: XListenerSet
      group: gateway.networking.x-k8s.io
  rules:
    - backendRefs:
        - name: httpbin
          port: 8000
EOF

  3. Verify that the HTTPRoute is applied successfully.

    kubectl get httproute/httpbin-https -n httpbin -o yaml

    Example output: Notice in the status section that the parentRef is either the Gateway or the ListenerSet, depending on how you attached the HTTPRoute.

    ...
status:
  parents:
  - conditions:
    - lastTransitionTime: "2025-04-29T20:48:51Z"
      message: ""
      observedGeneration: 3
      reason: Accepted
      status: "True"
      type: Accepted
    - lastTransitionTime: "2025-04-29T20:48:51Z"
      message: ""
      observedGeneration: 3
      reason: ResolvedRefs
      status: "True"
      type: ResolvedRefs
    controllerName: solo.io/gloo-gateway
  parentRef:
    group: gateway.networking.x-k8s.io
    kind: XListenerSet
    name: https-listenerset
    namespace: kgateway-system

  4. Verify that the listener now has a route attached.

    kubectl get gateway -n kgateway-system https -o yaml

    Example output:

    ...
listeners:
- attachedRoutes: 1
    kubectl get xlistenerset -n kgateway-system https-listenerset -o yaml

    Example output:

    ...
listeners:
- attachedRoutes: 1

    Note that because the HTTPRoute is attached to the ListenerSet, the Gateway does not show the route in its status.

    kubectl get gateway -n kgateway-system https -o yaml

    Example output:

    ...
listeners:
- attachedRoutes: 0

    If you create another HTTPRoute that attaches to the Gateway and uses the same listener as the ListenerSet, then the route is reported in the status of both the Gateway (attachedRoutes: 1) and the ListenerSet (attachedRoutes: 2).

  5. Get the external address of the gateway and save it in an environment variable. Note that it might take a few seconds for the gateway address to become available. 

    export INGRESS_GW_ADDRESS=$(kubectl get svc -n kgateway-system https -o jsonpath="{.status.loadBalancer.ingress[0]['hostname','ip']}")
echo $INGRESS_GW_ADDRESS   
    kubectl port-forward svc/https -n kgateway-system 8443:443

  6. Send a request to the httpbin app. Verify that you see the TLS handshake and that you get back a 200 HTTP response code. 

    curl -vik --resolve "https.example.com:443:${INGRESS_GW_ADDRESS}"  https://https.example.com:443/anything \
  --cert example_certs/client.example.com.crt \
  --key example_certs/client.example.com.key \
  --cacert example_certs/example.com.crt 
    curl -vik --resolve "https.example.com:443:$(dig +short $INGRESS_GW_ADDRESS | head -n1)"  https://https.example.com:443/anything \
  --cert example_certs/client.example.com.crt \
  --key example_certs/client.example.com.key \
  --cacert example_certs/example.com.crt 
    curl -vik --connect-to https.example.com:443:localhost:8443 https://https.example.com:443/anything \
  --cert example_certs/client.example.com.crt \
  --key example_certs/client.example.com.key \
  --cacert example_certs/example.com.crt

    Example output:

    * ALPN: curl offers h2,http/1.1
* (304) (OUT), TLS handshake, Client hello (1):
* (304) (IN), TLS handshake, Server hello (2):
* (304) (IN), TLS handshake, Unknown (8):
* (304) (IN), TLS handshake, Request CERT (13):
* (304) (IN), TLS handshake, Certificate (11):
* (304) (IN), TLS handshake, CERT verify (15):
* (304) (IN), TLS handshake, Finished (20):
* (304) (OUT), TLS handshake, Certificate (11):
* (304) (OUT), TLS handshake, CERT verify (15):
* (304) (OUT), TLS handshake, Finished (20):
* SSL connection using TLSv1.3 / AEAD-CHACHA20-POLY1305-SHA256 / [blank] / UNDEF
* ALPN: server accepted h2
* Server certificate:
*  subject: CN=*; O=any domain
*  issuer: O=any domain; CN=*
*  SSL certificate verify result: unable to get local issuer certificate (20), continuing   anyway.
* using HTTP/2
* [HTTP/2] [1] OPENED stream for https://https.example.com:443/anything
* [HTTP/2] [1] [:method: GET]
* [HTTP/2] [1] [:scheme: https]
* [HTTP/2] [1] [:authority: https.example.com]
* [HTTP/2] [1] [:path: /anything]
* [HTTP/2] [1] [user-agent: curl/8.7.1]
* [HTTP/2] [1] [accept: */*]
> GET /anything HTTP/2
> Host: https.example.com
> User-Agent: curl/8.7.1
> Accept: */*
> 
* Request completely sent off
< HTTP/2 200 
HTTP/2 200 
...
{
  "args": {},
  "headers": {
    "Accept": [
      "*/*"
    ],
    "Host": [
      "https.example.com"
    ],
    "User-Agent": [
      "curl/8.7.1"
    ],
    "X-Envoy-Expected-Rq-Timeout-Ms": [
      "15000"
    ],
    "X-Forwarded-Proto": [
      "https"
    ],
    "X-Request-Id": [
      "01ef350c-4587-4350-aa0e-0712fee757b9"
    ]
  },
  "url": "https://https.example.com/anything",
  ...
}

Cleanup

  1. Remove the routing resources for the HTTPS route, including the Kubernetes secret that holds the TLS certificate and key.

    kubectl delete httproute,gateway,secret -A -l gateway=https
    kubectl delete httproute,xlistenerset,gateway,secret -A -l gateway=https

  2. Remove the example_certs directory that stores your TLS credentials.

    rm -rf example_certs
HTTPSSNI