Transport Layer Security (TLS)

The Ambassador Edge Stack's robust TLS support exposes configuration options for different TLS use cases including:

`Host`

As explained in the Host reference, a Host represents a domain in Ambassador and defines how TLS is managed on that domain. In the Ambassador Edge Stack, the simplest configuration of a Host will enable TLS with a self-signed certificate and redirect cleartext traffic to HTTPS.

Automatic TLS with ACME

With the Ambassador Edge Stack, the Host can be configured to completely manage TLS by requesting a certificate from a Certificate Authority using the ACME HTTP-01 challenge.

After creating a DNS record, configuring the Ambassador Edge Stack to get a certificate from the default CA Let's Encrypt is as simple as providing a hostname and your email for the certificate:

---
apiVersion: getambassador.io/v2
kind: Host
metadata:
  name: example-host
spec:
  hostname: host.example.com
  acmeProvider:
    authority: https://acme-v02.api.letsencrypt.org/directory # Optional: The CA you want to get your certificate from. Defaults to Let's Encrypt
    email: julian@example.com

Ambassador will now request a certificate from the CA and store it in a secret in the same namespace as the Host.

Bring your own certificate

For both the Ambassador Edge Stack and API Gateway, the Host can read a certificate from a Kubernetes secret and use that certificate to terminate TLS on a domain.

The following will configure Ambassador to grab a certificate from a secret named host-secret and use that secret for terminating TLS on the host.example.com domain:

---
apiVersion: getambassador.io/v2
kind: Host
metadata:
  name: example-host
spec:
  hostname: host.example.com
  acmeProvider:
    authority: none
  tlsSecret:
    name: host-secret

Ambassador will now use the certificate in host-secret to terminate TLS.

`Host` and `TLSContext`

The Host will configure basic TLS termination settings in Ambassador. If you need more advanced TLS options on a domain, such as setting the minimum TLS version, you can do it in one of the following ways.

Create a TLSContext with the name {{HOST}}-context
Link a TLSContext to the Host
Specify TLS configuration in the Host

Create a `TLSContext` with the name `{{HOST}}-context`

You can create a TLSContext with the name {{NAME_OF_HOST}}-context, hosts set to the same hostname, and secret set to the same tlsSecret.

For example, to enforce a minimum TLS version on the Host above, create a TLSContext named example-host-context with the following configuration:

---
apiVersion: getambassador.io/v2
kind: TLSContext
metadata:
  name: example-host-context
spec:
  hosts:
  - host.example.com
  secret: host-secret
  min_tls_version: v1.2

Full reference for all options available to the TLSContext can be found below.

Link a `TLSContext` to the Host

You can create a new TLSContext with the desired configuration and link it to the Host via the tlsContext field.

For example, to enforce a minimum TLS version on the Host above, create a TLSContext with any name with the following configuration:

---
apiVersion: getambassador.io/v2
kind: TLSContext
metadata:
  name: min-tls-context
spec:
  secret: min-secret
  min_tls_version: v1.2

and link it to the Host via the tlsContext field as shown:

---
apiVersion: getambassador.io/v2
kind: Host
metadata:
  name: example-host
spec:
  hostname: host.example.com
  acmeProvider:
    authority: none
  tlsSecret:
    name: min-secret
  tlsContext:
    name: min-tls-context

Note: Any hosts or secret in the TLSContext must be the compatible with the Host to which it is being linked.

Specify TLS configuration in the Host

You can specify TLS configuration directly in the Host via the tls field.

For example, to enforce a minimum TLS version on the Host, the configuration will look like this:

---
apiVersion: getambassador.io/v2
kind: Host
metadata:
  name: example-host
spec:
  hostname: host.example.com
  acmeProvider:
    authority: none
  tlsSecret:
    name: min-secret
  tls:
    min_tls_version: v1.2

The following fields are accepted in the tls field:

tls:
  cert_chain_file: # <type: string>
  private_key_file: # <type: string>
  ca_secret: # <type: string>
  cacert_chain_file: # <type: string>
  alpn_protocols: # <type: string>
  cert_required: # <type: bool>
  min_tls_version: # <type: string>
  max_tls_version: # <type: string>
  cipher_suites: # <type: array of strings>
  ecdh_curves: # <type: array of strings>
  redirect_cleartext_from: # <type: int32>
  sni: # <type: string>

See TLSContext below to read more on the description of these fields.

TLSContext

The TLSContext is used to configure advanced TLS options in Ambassador. Remember, a TLSContext should always be paired with a Host.

A full schema of the TLSContext can be found below with descriptions of the different configuration options.

---
apiVersion: getambassador.io/v2
kind: TLSContext
metadata:
  name: example-host-context
spec:
  # 'hosts' defines the hosts for which this TLSContext is relevant.
  # It ties into SNI. A TLSContext without "hosts" is useful only for 
  # originating TLS. 
  # type: array of strings
  #
  # hosts: []
  # 'sni' defines the SNI string to use on originated connections.
  # type: string
  #
  # sni: None
  # 'secret' defines a Kubernetes Secret that contains the TLS certificate we
  # use for origination or termination. If not specified, Ambassador will look
  # at the value of cert_chain_file and private_key_file.
  # type: string
  #
  # secret: None
  # 'ca_secret' defines a Kubernetes Secret that contains the TLS certificate we
  # use for verifying incoming TLS client certificates.
  # type: string
  #
  # ca_secret: None
  # Tells Ambassador whether to interpret a "." in the secret name as a "." or 
  # a namespace identifier.
  # type: boolean
  #
  # secret_namespacing: true
  # If you set 'redirect_cleartext_from' to a port number, HTTP traffic
  # to that port will be redirected to HTTPS traffic. Make sure that the
  # port number you specify matches the port on which Ambassador is
  # listening!
  # redirect_cleartext_from: 8080
  # 'cert_required' can be set to true to _require_ TLS client certificate
  # authentication.
  # type: boolean
  #
  # cert_required: false
  # 'alpn_protocols' is used to enable the TLS ALPN protocol. It is required
  # if you want to do GRPC over TLS; typically it will be set to "h2" for that
  # case.
  # type: string (comma-separated list)
  #
  # alpn_protocols: None
  # 'min_tls_version' sets the minimum acceptable TLS version: v1.0, v1.1,
  # v1.2, or v1.3. It defaults to v1.0.
  # min_tls_version: v1.0
  # 'max_tls_version' sets the maximum acceptable TLS version: v1.0, v1.1,
  # v1.2, or v1.3. It defaults to v1.3.
  # max_tls_version: v1.3
  # Tells Ambassador to load TLS certificates from a file in its container.
  # type: string
  #
  # cert_chain_file: None
  # private_key_file: None
  # cacert_chain_file: None

`alpn_protocols`

The alpn_protocols setting configures the TLS ALPN protocol. To use gRPC over TLS, set alpn_protocols: h2. If you need to support HTTP/2 upgrade from HTTP/1, set alpn_protocols: h2,http/1.1 in the configuration.

HTTP/2 Support

The alpn_protocols setting is also required for HTTP/2 support.

apiVersion: getambassador.io/v2
kind:  TLSContext
metadata:
  name:  tls
spec:
  secret: ambassador-certs
  hosts: ["*"]
  alpn_protocols: h2[, http/1.1]

Without setting alpn_protocols as shown above, HTTP2 will not be available via negotiation and will have to be explicitly requested by the client.

If you leave off http/1.1, only HTTP2 connections will be supported.

TLS Parameters

The min_tls_version setting configures the minimum TLS protocol version that Ambassador Edge Stack will use to establish a secure connection. When a client using a lower version attempts to connect to the server, the handshake will result in the following error: tls: protocol version not supported.

The max_tls_version setting configures the maximum TLS protocol version that Ambassador Edge Stack will use to establish a secure connection. When a client using a higher version attempts to connect to the server, the handshake will result in the following error: tls: server selected unsupported protocol version.

The cipher_suites setting configures the supported cipher list when negotiating a TLS 1.0-1.2 connection. This setting has no effect when negotiating a TLS 1.3 connection. When a client does not support a matching cipher a handshake error will result.

The ecdh_curves setting configures the supported ECDH curves when negotiating a TLS connection. When a client does not support a matching ECDH a handshake error will result.

---
apiVersion: getambassador.io/v2
kind:  TLSContext
metadata:
  name:  tls
spec:
  hosts: ["*"]
  secret: ambassador-certs
  min_tls_version: v1.0
  max_tls_version: v1.3
  cipher_suites:
  - "[ECDHE-ECDSA-AES128-GCM-SHA256|ECDHE-ECDSA-CHACHA20-POLY1305]"
  - "[ECDHE-RSA-AES128-GCM-SHA256|ECDHE-RSA-CHACHA20-POLY1305]"
  ecdh_curves:
  - X25519
  - P-256

TLS `Module` (Deprecated)

The TLS Module is deprecated. TLSContext should be used when using Ambassador version 0.50.0 and above.

For users of the Ambassador Edge Stack, see the Host CRD reference for more information.

---
apiVersion: getambassador.io/v2
kind:  Module
metadata:
  name:  tls
spec:
  config:
    # The 'server' block configures TLS termination. 'enabled' is the only
    # required element.
    server:
      # If 'enabled' is not True, TLS termination will not happen.
      enabled: True
      # If you set 'redirect_cleartext_from' to a port number, HTTP traffic
      # to that port will be redirected to HTTPS traffic. Make sure that the
      # port number you specify matches the port on which Ambassador is
      # listening!
      # redirect_cleartext_from: 8080
      # These are optional. They should not be present unless you are using
      # a custom Docker build to install certificates onto the container
      # filesystem, in which case YOU WILL STILL NEED TO SET enabled: True
      # above.
      #
      # cert_chain_file: /etc/certs/tls.crt   # remember to set enabled!
      # private_key_file: /etc/certs/tls.key  # remember to set enabled!
      # Enable TLS ALPN protocol, typically HTTP2 to negotiate it with
      # HTTP2 clients over TLS.
      # This must be set to be able to use grpc over TLS.
      # alpn_protocols: h2
    # The 'client' block configures TLS client-certificate authentication.
    # 'enabled' is the only required element.
    client:
      # If 'enabled' is not True, TLS client-certificate authentication will
      # not happen.
      enabled: False
      # If 'cert_required' is True, TLS client certificates will be required
      # for every connection.
      # cert_required: False
      # This is optional. It should not be present unless you are using
      # a custom Docker build to install certificates onto the container
      # filesystem, in which case YOU WILL STILL NEED TO SET enabled: True
      # above.
      #
      # cacert_chain_file: /etc/cacert/tls.crt  # remember to set enabled!

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