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Proxy Extensions

Current Status: Alpha (Since v2.7.0)

Overview

With UI extensions it is possible to enhance Argo CD web interface to provide valuable data to the user. However the data is restricted to the resources that belongs to the Application. With proxy extensions it is also possible to add additional functionality that have access to data provided by backend services. In this case Argo CD API server acts as a reverse-proxy authenticating and authorizing incoming requests before forwarding to the backend service.

Configuration

As proxy extension is in Alpha phase, the feature is disabled by default. To enable it, it is necessary to configure the feature flag in Argo CD command parameters. The easiest way to to properly enable this feature flag is by adding the server.enable.proxy.extension key in the existing argocd-cmd-params-cm. For example:

apiVersion: v1
kind: ConfigMap
metadata:
  name: argocd-cmd-params-cm
  namespace: argocd
data:
  server.enable.proxy.extension: "true"

Once the proxy extension is enabled, it can be configured in the main Argo CD configmap (argocd-cm).

The example below demonstrates all possible configurations available for proxy extensions:

apiVersion: v1
kind: ConfigMap
metadata:
  name: argocd-cm
  namespace: argocd
data:
  extension.config: |
    extensions:
    - name: httpbin
      backend:
        connectionTimeout: 2s
        keepAlive: 15s
        idleConnectionTimeout: 60s
        maxIdleConnections: 30
        services:
        - url: http://httpbin.org
          headers:
          - name: some-header
            value: '$some.argocd.secret.key'
          cluster:
            name: some-cluster
            server: https://some-cluster

Note: There is no need to restart Argo CD Server after modifiying the extension.config entry in Argo CD configmap. Changes will be automatically applied. A new proxy registry will be built making all new incoming extensions requests (<argocd-host>/extensions/*) to respect the new configuration.

Every configuration entry is explained below:

extensions (list)

Defines configurations for all extensions enabled.

extensions.name (string)

(mandatory)

Defines the endpoint that will be used to register the extension route. For example, if the value of the property is extensions.name: my-extension then the backend service will be exposed under the following url:

<argocd-host>/extensions/my-extension

extensions.backend.connectionTimeout (duration string)

(optional. Default: 2s)

Is the maximum amount of time a dial to the extension server will wait for a connect to complete.

extensions.backend.keepAlive (duration string)

(optional. Default: 15s)

Specifies the interval between keep-alive probes for an active network connection between the API server and the extension server.

extensions.backend.idleConnectionTimeout (duration string)

(optional. Default: 60s)

Is the maximum amount of time an idle (keep-alive) connection between the API server and the extension server will remain idle before closing itself.

extensions.backend.maxIdleConnections (int)

(optional. Default: 30)

Controls the maximum number of idle (keep-alive) connections between the API server and the extension server.

extensions.backend.services (list)

Defines a list with backend url by cluster.

extensions.backend.services.url (string)

(mandatory)

Is the address where the extension backend must be available.

extensions.backend.services.headers (list)

If provided, the headers list will be added on all outgoing requests for this service config. Existing headers in the incoming request with the same name will be overriden by the one in this list. Reserved header names will be ignored (see the headers below).

extensions.backend.services.headers.name (string)

(mandatory)

Defines the name of the header. It is a mandatory field if a header is provided.

extensions.backend.services.headers.value (string)

(mandatory)

Defines the value of the header. It is a mandatory field if a header is provided. The value can be provided as verbatim or as a reference to an Argo CD secret key. In order to provide it as a reference, it is necessary to prefix it with a dollar sign.

Example:

value: '$some.argocd.secret.key'

In the example above, the value will be replaced with the one from the argocd-secret with key 'some.argocd.secret.key'.

extensions.backend.services.cluster (object)

(optional)

If provided, and multiple services are configured, will have to match the application destination name or server to have requests properly forwarded to this service URL. If there are multiple backends for the same extension this field is required. In this case at least one of the two will be required: name or server. It is better to provide both values to avoid problems with applications unable to send requests to the proper backend service. If only one backend service is configured, this field is ignored, and all requests are forwarded to the configured one.

extensions.backend.services.cluster.name (string)

(optional)

It will be matched with the value from Application.Spec.Destination.Name

extensions.backend.services.cluster.server (string)

(optional)

It will be matched with the value from Application.Spec.Destination.Server.

Usage

Once a proxy extension is configured it will be made available under the /extensions/<extension-name> endpoint exposed by Argo CD API server. The example above will proxy requests to <apiserver-host>/extensions/httpbin/ to http://httpbin.org.

The diagram below illustrates an interaction possible with this configuration:

                                              ┌─────────────┐
                                              │ Argo CD UI  │
                                              └────┬────────┘
                                                   │  ▲
  GET <apiserver-host>/extensions/httpbin/anything │  │ 200 OK
            + authn/authz headers                  │  │
                                                   ▼  │
                                            ┌─────────┴────────┐
                                            │Argo CD API Server│
                                            └──────┬───────────┘
                                                   │  ▲
                   GET http://httpbin.org/anything │  │ 200 OK
                                                   │  │
                                                   ▼  │
                                             ┌────────┴────────┐
                                             │ Backend Service │
                                             └─────────────────┘

Incoming Request Headers

Note that Argo CD API Server requires additional HTTP headers to be sent in order to enforce if the incoming request is authenticated and authorized before being proxied to the backend service. The headers are documented below:

Argo CD UI keeps the authentication token stored in a cookie (argocd.token). This value needs to be sent in the Cookie header so the API server can validate its authenticity.

Example: 

Cookie: argocd.token=eyJhbGciOiJIUzI1Ni...

The entire Argo CD cookie list can also be sent. The API server will only use the argocd.token attribute in this case.

Argocd-Application-Name (mandatory)

This is the name of the project for the application for which the extension is being invoked. The header value must follow the format: "<namespace>:<app-name>".

Example:

Argocd-Application-Name: namespace:app-name

Argocd-Project-Name (mandatory)

The logged in user must have access to this project in order to be authorized.

Example:

Argocd-Project-Name: default

Argo CD API Server will ensure that the logged in user has the permission to access the resources provided by the headers above. The validation is based on pre-configured Argo CD RBAC rules. The same headers are also sent to the backend service. The backend service must also validate if the validated headers are compatible with the rest of the incoming request.

Outgoing Requests Headers

Requests sent to backend services will be decorated with additional headers. The outgoing request headers are documented below:

Argocd-Target-Cluster-Name

Will be populated with the value from app.Spec.Destination.Name if it is not empty string in the application resource.

Argocd-Target-Cluster-URL

Will be populated with the value from app.Spec.Destination.Server if it is not empty string is the Application resource.

Note that additional pre-configured headers can be added to outgoing request. See backend service headers section for more details.

Multi Backend Use-Case

In some cases when Argo CD is configured to sync with multiple remote clusters, there might be a need to call a specific backend service in each of those clusters. The proxy-extension can be configured to address this use-case by defining multiple services for the same extension. Consider the following configuration as an example:

extension.config: |
  extensions:
  - name: some-extension
    backend:
      services:
      - url: http://extension-name.com:8080
        cluster
          name: kubernetes.local
      - url: https://extension-name.ppd.cluster.k8s.local:8080
        cluster
          server: user@ppd.cluster.k8s.local

In the example above, the API server will inspect the Application destination to verify which URL should be used to proxy the incoming request to.

Security

When a request to /extensions/* reaches the API Server, it will first verify if it is authenticated with a valid token. It does so by inspecting if the Cookie header is properly sent from Argo CD UI extension.

Once the request is authenticated it is then verified if the user has permission to invoke this extension. The permission is enforced by Argo CD RBAC configuration. The details about how to configure the RBAC for proxy-extensions can be found in the RBAC documentation page.

Once the request is authenticated and authorized by the API server, it is then sanitized before being sent to the backend service. The request sanitization will remove sensitive information from the request like the Cookie and Authorization headers.

A new Authorization header can be added to the outgoing request by defining it as a header in the extensions.backend.services.headers configuration. Consider the following example:

extension.config: |
  extensions:
  - name: some-extension
    backend:
      services:
      - url: http://extension-name.com:8080
        headers:
        - name: Authorization
          value: '$some-extension.authorization.header'

In the example above, all requests sent to http://extension-name.com:8080 will have an additional Authorization header. The value of this header will be the one from the argocd-secret with key some-extension.authorization.header