Configuring HAProxy in Front of Admin Router

You can use HAProxy to set up an HTTP proxy in front of the DC/OS Admin Router. This was previously useful to allow Admin Router to present a custom server certificate to user agents connecting to the cluster via HTTPS. From DC/OS 2.2 this can be achieved more directly using custom external certificates.

The HTTP Proxy must perform on-the-fly HTTP request and response header modification, because DC/OS is not aware of the custom hostname and port that is being used by user agents to address the HTTP proxy.

The following instructions provide a tested HAProxy configuration example that handles the named request/response rewriting. This example ensures that the communication between HAProxy and DC/OS Admin Router is TLS-encrypted.

Install HAProxy 1.6.9.

Create an HAProxy configuration for DC/OS. This example is for a DC/OS cluster on AWS. For more information on HAProxy configuration parameters, see the documentation.

You can find your task IP by using the agent IP address DNS entry.

<taskname>.<framework_name>.agentip.dcos.thisdcos.directory

Where:

taskname: The name of the task.
framework_name: The name of the framework, if you are unsure, it is likely marathon.

global
  daemon
  log 127.0.0.1 local0
  log 127.0.0.1 local1 notice
  maxconn 20000
  pidfile /var/run/haproxy.pid
defaults
  log            global
  option         dontlog-normal
  mode		 http
  retries             3
  maxconn          20000
  timeout connect  5000
  timeout client  50000
  timeout server  50000

frontend http
  # Bind on port 9090. HAProxy will listen on port 9090 on each
  # available network for new HTTP connections.
  bind 0.0.0.0:9090
  # Specify your own server certificate chain and associated private key.
  # See https://cbonte.github.io/haproxy-dconv/configuration-1.6.html#5.1-crt
  # bind *:9091 ssl crt /path/to/browser-trusted.crt
  #
  # Name of backend configuration for DC/OS.
  default_backend dcos

  # Store request Host header temporarily in transaction scope
  # so that its value is accessible during response processing.
  # Note: RFC 7230 requires clients to send the Host header and
  # specifies it to contain both, host and port information.
  http-request set-var(txn.request_host_header) req.hdr(Host)

  # Overwrite Host header to 'dcoshost'. This makes the Location
  # header in DC/OS Admin Router upstream responses contain a
  # predictable hostname (NGINX uses this header value when
  # constructing absolute redirect URLs). That value is used
  # in the response Location header rewrite logic (see regular
  # expression-based rewrite in the backend section below).
  http-request set-header Host dcoshost

backend dcos
  # Option 1: use TLS-encrypted communication with DC/OS Admin Router and
  # perform server certificate verification (including hostname verification).
  # If you are using the community-supported version of DC/OS, you must
  # configure Admin Router with a custom TLS server certificate, see
  # /mesosphere/dcos/2.2/administering-clusters/. This step
  # is not required for DC/OS Enterprise.
  #
  # Explanation for the parameters in the following `server` definition line:
  #
  # 1.2.3.4:443
  #
  #   IP address and port that HAProxy uses to connect to DC/OS Admin
  #   Router. This needs to be adjusted to your setup.
  #
  #
  # ssl verify required
  #
  #   Instruct HAProxy to use TLS, and to error out if server certificate
  #   verification fails.
  #
  # ca-file dcos-ca.crt
  #
  #   The local file `dcos-ca.crt` is expected to contain the CA certificate
  #   that Admin Router's certificate will be verified against. It must be
  #   retrieved out-of-band (on Mesosphere DC/OS Enterprise this can be
  #   obtained via https://dcoshost/ca/dcos-ca.crt)
  #
  # verifyhost frontend-xxx.eu-central-1.elb.amazonaws.com
  #
  #   When verifying the TLS certificate presented by DC/OS Admin Router,
  #   perform hostname verification using the hostname specified here
  #   (expect the server certificate to contain a DNSName SAN that is
  #   equivalent to the hostname defined here). The hostname shown here is
  #   just an example and needs to be adjusted to your setup.

  server dcos-1 1.2.3.4:443 ssl verify required ca-file dcos-ca.crt verifyhost frontend-xxx.eu-central-1.elb.amazonaws.com

  # Option 2: use TLS-encrypted communication with DC/OS Admin Router, but do
  # not perform server certificate verification (warning: this is insecure, and
  # we hope that you know what you are doing).
  # server dcos-1 1.2.3.4:443 ssl verify none
  #
  # Rewrite response Location header if it contains an absolute URL
  # pointing to the 'dcoshost' host: replace 'dcoshost' with original
  # request Host header (containing hostname and port).
  http-response replace-header Location https?://dcoshost((/.*)?) "http://%[var(txn.request_host_header)]\1"

Start HAProxy with these settings.

Configuring HAProxy in Front of Admin Router

Using the HAProxy to set up an HTTP proxy for the DC/OS Admin Router