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- Document option to host user sessions on a load balancer node.

\label{Domain_Configuration_Load_Balancing}

A ``Dedicated Load Balancer(s)'' option will be included in the list of modifiable domain settings if your LON-CAPA domain contains more than one server or VM.

If you chose to designate one of your servers/VMs as a load balancer, you can configure balancing behavior as follows:

\begin{itemize}

\item Default destinations

This determines which of your servers/VMs will host user sessions (by default) after log-in via the load balancer server/VM.  You can separate destinations into ``primary'' and ``default''.  
The least loaded of the primary servers/VMs will be selected, unless all primary servers/VMs are considered 100\% loaded, in which case the least loaded of the default servers/VMs will be selected.

You can also permit hosting on the load balancer node itself, by selecting primary or default for ``Hosting on balancer itself'', in which case determination of least loaded for the particular grouping will also include the load balancer.

\item User affiliation -- overrides

The choice of server/VM to host user sessions for particular types of user can be further configured, by choosing an action for particular user types. The chosen action will override the default behavior.  The choice of user types includes the various affiliations defined for the institution (e.g.,  Faculty, Staff etc.).  If users are not affiliated with any institutional group, they can be accommodated within the default {}``Other users'' type which is provided automatically. If no status types are defined for your domain, this default group is entitled {}``All users''.

In addition to type based on affiliation, there are additional types:

\begin{itemize}

\item Advanced users from domain (i.e., users with author, coordinator, instructor or administrator roles)

\item Users from domain with author role

\end{itemize}

If an institution runs a library server with multiple domains, the server selected to be the load balancer can be different from the particular domain for which balancing is being configured. Two other additional types are available where the load balancer's domain and domain being configured match:

\begin{itemize}

\item Users not from domain, but with a home server matching institution's web address (e.g., yourcollege.edu)

\item Users not from domain or with a home server matching institution's web address web address

\end{itemize}

In all but the last case, the options available are:

\begin{itemize}

\item Offloads to default destinations

\item Offloads to user's home server

\item  Offloads to a specific server in the user's domain (select froma dropdown list)

\item No offload
 
\end{itemize}

In the last case (i.e., users whose home domain is not on any of the servers/VMs you manage), the options are:
(a) Offloads to default destinations, (b) Offloads to user's home server, (c) Offloads to Load Balancer in user's domain,
(d) No offload

\item User's remote IP address changes between log-in to load balancer server, and session initialization on offload server  

LON-CAPA expects the remote IP address of the client web request to be the same at the authentication stage on the load balancer, and then subsequently, following 
attempted session migration to the offload server. Where IPs do not match (e.g., a user is accessing LON-CAPA using an internet connection provided by a 
cellular network, where IP addresses are pooled and can change between requests), you can set how that situation should be handled.  The options are:

\begin{itemize}

\item Session hosted on Load Balancer, after re-authentication

\item Session hosted on offload server, after re-authentication

\item Session hosted on a specified server (selected from the domain's servers), after re-authentication 

\end{itemize}

If the load balancing server's domain and the domain being configured are the same, you will select one of these options separately for
(a) Single Sign On (SSO) users from your domain, and also (b) for both non-SSO users from your domain, and for users from other domains in the LON-CAPA network (if you have joined a cluster).  If your institution maintains multiple domains then a load balancer can have a different domain from the domain you are currently configuring.  In that instance you will select one of these options separately for (a) SSO users from your domain and (b) non-SSO users from your domain.

\end{itemize}