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TLS configuration

Argo CD provides two inbound TLS endpoints that can be configured:

  • The user-facing endpoint of the argocd-server workload which serves the UI and the API
  • The endpoint of the argocd-repo-server, which is accessed by argocd-server and argocd-application-controller workloads to request repository operations.

By default, and without further configuration, both of these endpoints will be set-up to use an automatically generated, self-signed certificate. However, most users will want to explicitly configure the certificates for these TLS endpoints, possibly using automated means such as cert-manager or using their own dedicated Certificate Authority.

Configuring TLS for argocd-server

Inbound TLS options for argocd-server

You can configure certain TLS options for the argocd-server workload by setting command line parameters. The following parameters are available:

Parameter Default Description
--insecure false Disables TLS completely
--tlsminversion 1.2 The minimum TLS version to be offered to clients
--tlsmaxversion 1.3 The maximum TLS version to be offered to clients
--tlsciphers TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384:TLS_RSA_WITH_AES_256_GCM_SHA384 A colon separated list of TLS cipher suites to be offered to clients

TLS certificates used by argocd-sever

There are two ways to configure the TLS certificates used by argocd-server:

  • Setting the tls.crt and tls.key keys in the argocd-server-tls secret to hold PEM data of the certificate and the corresponding private key. The argocd-server-tls secret may be of type tls, but does not have to be.
  • Setting the tls.crt and tls.key keys in the argocd-secret secret to hold PEM data of the certificate and the corresponding private key. This method is considered deprecated, and only exists for purposes of backwards compatiblity. Changing argocd-secret should not be used to override the TLS certificate anymore.

Argo CD decides which TLS certificate to use for the endpoint of argocd-server as follows:

  • If the argocd-server-tls secret exists and contains a valid key pair in the tls.crt and tls.key keys, this will be used for the certificate of the endpoint of argocd-server.
  • Otherwise, if the argocd-secret secret contains a valid key pair in the tls.crt and tls.key keys, this will be used as certificate for the endpoint of argocd-server.
  • If no tls.crt and tls.key keys are found in neither of the two mentioned secrets, Argo CD will generate a self-signed certificate and persist it in the argocd-secret secret.

The argocd-server-tls secret contains only information for TLS configuration to be used by argocd-server and is safe to be managed via third-party tools such as cert-manager or SealedSecrets

To create this secret manually from an existing key pair, you can use kubectl:

kubectl create -n argocd secret tls argocd-server-tls \
  --cert=/path/to/cert.pem \
  --key=/path/to/key.pem

Argo CD will pick up changes to the argocd-server-tls secret automatically and will not require restart of the pods to use a renewed certificate.

Configuring inbound TLS for argocd-repo-server

Inbound TLS options for argocd-repo-server

You can configure certain TLS options for the argocd-repo-server workload by setting command line parameters. The following parameters are available:

Parameter Default Description
--disable-tls false Disables TLS completely
--tlsminversion 1.2 The minimum TLS version to be offered to clients
--tlsmaxversion 1.3 The maximum TLS version to be offered to clients
--tlsciphers TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384:TLS_RSA_WITH_AES_256_GCM_SHA384 A colon separated list of TLS cipher suites to be offered to clients

Inbound TLS certificates used by argocd-sever

To configure the TLS certificate used by the argocd-repo-server workload, create a secret named argocd-repo-server-tls in the namespace where Argo CD is running in with the certificate's key pair stored in tls.crt and tls.key keys. If this secret does not exist, argocd-repo-server will generate and use a self-signed certificate.

To create this secret, you can use kubectl:

kubectl create -n argocd secret tls argocd-repo-server-tls \
  --cert=/path/to/cert.pem \
  --key=/path/to/key.pem

Please note, that as opposed to argocd-server, the argocd-repo-server is not able to pick up changes to this secret automatically. If you create (or update) this secret, the argocd-repo-server pods need to be restarted.

Also note, that the certificate should be issued with the correct SAN entries for the argocd-repo-server, containing at least the entries for DNS:argocd-repo-server and DNS:argocd-repo-server.argo-cd.svc depending on how your workloads connect to the repository server.

Configuring TLS between Argo CD components

Configuring TLS to argocd-repo-server

Both argocd-server and argocd-application-controller communicate with the argocd-repo-server using a gRPC API over TLS. By default, argocd-repo-server generates a non-persistant, self signed certificate to use for its gRPC endpoint on startup. Because the argocd-repo-server has no means to connect to the K8s control plane API, this certificate is not being available to outside consumers for verification. Both, the argocd-server and argocd-application-server will use a non-validating connection to the argocd-repo-server for this reason.

To change this behavior to be more secure by having the argocd-server and argocd-application-controller validate the TLS certificate of the argocd-repo-server endpoint, the following steps need to be performed:

  • Create a persistent TLS certificate to be used by argocd-repo-server, as shown above
  • Restart the argocd-repo-server pod(s)
  • Modify the pod startup parameters for argocd-server and argocd-application-controller to include the --repo-server-strict-tls parameter.

The argocd-server and argocd-application-controller workloads will now validate the TLS certificate of the argocd-repo-server by using the certificate stored in the argocd-repo-server-tls secret.

Certificate expiry

Please make sure that the certificate has a proper life time. Keep in mind that when you have to replace the certificate, all workloads have to be restarted in order to properly work again.

Disabling TLS to argocd-repo-server

In some scenarios where mTLS through side-car proxies is involved (e.g. in a service mesh), you may want configure the connections between the argocd-server and argocd-application-controller to argocd-repo-server to not use TLS at all.

In this case, you will need to:

  • Configure argocd-repo-server with TLS on the gRPC API disabled by specifying the --disable-tls parameter to the pod container's startup arguments
  • Configure argocd-server and argocd-application-controller to not use TLS for connections to the argocd-repo-server by specifying the parameter --repo-server-plaintext to the pod container's startup arguments
  • Configure argocd-server and argocd-application-controller to connect to the side-car instead of directly to the argocd-repo-server service by specifying its address via the --repo-server <address> parameter

After this change, the argocd-server and argocd-application-controller will use a plain text connection to the side-car proxy, that will handle all aspects of TLS to the argocd-repo-server's TLS side-car proxy.