.. role:: green

.. role:: red

.. role:: blue

.. role:: orange


Ports & Health Checks
=====================

This area is for configuring the ports and protocols your balancer will use, along with
health checks it performs on the backend servers.


Health Checks
-------------

.. image:: ../_static/images/health_checks.png
    :target: ../_static/images/health_checks.png

In order to provide *high availability*, the balancer performs *health checks* on all 
backend servers, according to criteria set here.  The default is to simply check '/'
over plain HTTP expecting a 2xx response.

Backend servers failing health checks will automatically be set to :red:`DOWN` state and the 
balancer will stop sending traffic.  Checks continue, and when the backend server starts 
passing checks again, the balancer will set it back to :green:`UP` state and resume passing 
traffic.

You can click :guilabel:`Edit` to modify your checks, the parameters are described below:

Port
  The port to check.  This must be open on all backend servers.

Protocol
  * **TCP**:
    Only check if the port is open ("Layer 4").  The "Path" option (described below) is ignored.  
    This is the only check available when balancing protocols other than HTTP.
    
  * **HTTP**:
    Plain HTTP (protocol-aware, "Layer 7").  Will make a request to "Path", expecting a 
    2xx response.

  * **HTTPS**:
    Same as HTTP, but use TLS.  

.. Note::
   TLS certificates are not verified for connections to backend servers.

Path
    With HTTP or HTTPS, /path/to/check

Interval
    Number of seconds between checks.

Timeout before failure
    Number of seconds to wait for a response before failing.  This must be less than Interval.

Number of failed attempts (fall)
    Number of failed checks before setting a backend server :red:`DOWN`.

Number of successful attempts (rise)
    Number of successful checks before setting a :red:`DOWN` server back :green:`UP`.


.. Note::
   Health checks are run across *all backend servers* at the interval specified.


Ports
-----

.. image:: ../_static/images/ports.png
    :target: ../_static/images/ports.png

Balancer ports consist of two parts: a *frontend*, which is a port open on it's Public IPv4 address,
and a *backend* which is the "destination" port it sends traffic to on the backend servers.  Additionally, 
just like health checks you specify a protocol, and optionally a certificate.

Add a port
++++++++++

To add a port, click :guilabel:`Add port`.  Set the parameters in the form that opens:

Protocol
  * **TCP**:
    Direct TCP connection.  This is the simplest and also used when forwarding protocols 
    other than HTTP.

  * **HTTP**:
    Plain HTTP, protocol aware so options under :doc:`settings <settings>` also work (SSL Redirect, 
    Cookies, etc.)

  * **HTTPS**:
    Same as HTTP but with TLS.  If HTTPS is selected, another dropdown appears: "Certificate".
    If "Passthrough" is selected, TLS is passed through to be terminated and verified on each 
    backend server.  If a :doc:`certificate <certificates>` is available, it can be selected here to 
    terminate TLS *at the load balancer* instead.  This is typically more efficient as you only need 
    to worry about maintaining the one certificate on the balancer, as opposed to one on every 
    backend server.

.. Note::
   If a frontend port is added that matches an existing frontend port, it will simply update the 
   existing port.