Rotate TLS certificates

This page describes

Root certificate rotation

Whenever the CA's configuration is updated in a way that causes the root key to change, a special rotation process will be triggered in order to smoothly transition to the new certificate. This rotation is automatically orchestrated by Consul.

If the current CA Provider doesn't support cross-signing, this process can't be followed. See Forced Rotation Without Cross-Signing.

This also automatically occurs when a completely different CA provider is configured (since this changes the root key). Therefore, this automatic rotation process can also be used to cleanly transition between CA providers. For example, updating the service mesh to use Vault instead of the built-in CA.

During rotation, an intermediate CA certificate is requested from the new root, which is then cross-signed by the old root. This cross-signed certificate is then distributed alongside any newly-generated leaf certificates used by the proxies once the new root becomes active, and provides a chain of trust back to the old root certificate in the event that a certificate signed by the new root is presented to a proxy that has not yet updated its bundle of trusted root CA certificates to include the new root.

After the cross-signed certificate has been successfully generated and the new root certificate or CA provider has been set up, the new root becomes the active one and is immediately used for signing any new incoming certificate requests.

If we check the list CA roots endpoint after updating the configuration with a new root certificate, we can see both the old and new root certificates are present, and the currently active root has an intermediate certificate which has been generated and cross-signed automatically by the old root during the rotation process:

$ curl localhost:8500/v1/connect/ca/roots
{
    "ActiveRootID": "d2:2c:41:94:1e:50:04:ea:86:fc:08:d6:b0:45:a4:af:8a:eb:76:a0",
    "TrustDomain": "36cb52cd-4058-f811-0432-6798a240c5d3.consul",
    "Roots": [
        {
            "ID": "31:6c:06:fb:49:94:42:d5:e4:55:cc:2e:27:b3:b2:2e:96:67:3e:7e",
            "Name": "Consul CA Root Cert",
            "SerialNumber": 7,
            "SigningKeyID": "19:45:8b:30:a1:45:84:ae:23:52:db:8d:1b:ff:a9:09:db:fc:2a:72:39:ae:da:11:53:f4:37:5c:de:d1:68:d8",
            "ExternalTrustDomain": "a1499528-fbf6-df7b-05e5-ae81e1873fc4",
            "NotBefore": "2018-06-06T17:35:25Z",
            "NotAfter": "2028-06-03T17:35:25Z",
            "RootCert": "-----BEGIN CERTIFICATE-----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\nvC6jWPuqqMwmAiEAkvMadtwjtNU7m/AQRJrj1LeG3eXw7dWO8SlI2fEs0yY=\n-----END CERTIFICATE-----\n",
            "IntermediateCerts": null,
            "Active": false,
            "PrivateKeyType": "",
            "PrivateKeyBits": 0,
            "CreateIndex": 8,
            "ModifyIndex": 24
        },
        {
            "ID": "d2:2c:41:94:1e:50:04:ea:86:fc:08:d6:b0:45:a4:af:8a:eb:76:a0",
            "Name": "Consul CA Root Cert",
            "SerialNumber": 16238269036752183483,
            "SigningKeyID": "",
            "ExternalTrustDomain": "a1499528-fbf6-df7b-05e5-ae81e1873fc4",
            "NotBefore": "2018-06-06T17:37:03Z",
            "NotAfter": "2028-06-03T17:37:03Z",
            "RootCert": "-----BEGIN CERTIFICATE-----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\n-----END CERTIFICATE-----",
            "IntermediateCerts": [
                "-----BEGIN CERTIFICATE-----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\nAiEAwKBzEMcLd5kCBgFHNGyksRAMh/AGdEW859aL6z0u4gM=\n-----END CERTIFICATE-----\n"
            ],
            "Active": true,
            "PrivateKeyType": "",
            "PrivateKeyBits": 0,
            "CreateIndex": 24,
            "ModifyIndex": 24
        }
    ]
}

The old root certificate will be automatically removed once enough time has elapsed for any leaf certificates signed by it to expire.

Forced Rotation Without Cross-Signing

If the CA provider that is currently in use does not support cross-signing, then attempts to change the root key or CA provider will fail. This is to ensure operators don't make the change without understanding that there is additional risk involved.

It is possible to force the change to happen anyway by setting the ForceWithoutCrossSigning field in the CA configuration to true.

The downside is that all new certificates will immediately start being signed with the new root key, but it will take some time for agents throughout the cluster to observe the root CA change and reconfigure applications and proxies to accept certificates signed by this new root. This will mean connections made with a new certificate may fail for a short period after the CA change.

Typically all connected agents will have observed the new roots within seconds even in a large deployment so the impact should be contained. But it is possible for a disconnected, overloaded or misconfigured agent to not see the new root for an unbounded amount of time during which new connections to services on that host will fail. The issue will resolve as soon as the agent can reconnect to servers.

Currently both Consul and Vault CA providers do support cross signing. As more providers are added this documentation will list any that this section applies to.

Rotate TLS certificates for Consul on Kubernetes

As of Consul Helm version 0.29.0, if TLS is enabled, new TLS certificates for the Consul Server are issued every time the Helm chart is upgraded. These certificates are signed by the same CA and will continue to work as expected in the existing cluster.

Consul servers read the certificates from Kubernetes secrets during start-up and keep them in memory. In order to ensure the servers use the newer certificate, the server pods need to be restarted explicitly in a situation where helm upgrade does not restart the server pods.

To explicitly perform server certificate rotation, follow these steps:

Perform a helm upgrade:
```
$ helm upgrade consul hashicorp/consul --values /path/to/my/values.yaml
```
This should run the tls-init job that will generate new Server certificates.
Restart the Server pods following the steps here.