[Toolserver-l] Intention to add multiple web servers; some tools may need changing

[River Tarnell]

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Hi,

In the near future we plan to add an additional web server to the
Toolserver.  This will provide redundancy if either server fails, as
well as increasing capacity.  Each server will be identically configured
(with the same OS, software, etc.), and HTTP requests will be
distributed evenly between the systems.

Some tools may require changes to function correctly in this
environment:

* Any tool which stores data on a local disk (e.g. /tmp or /var/tmp)
  and expects to retrieve the data in a different request may find the
  data is not present if the subsequent request runs on a different web
  server.  To fix this, such data should be stored in a location
  accessible from all systems (e.g. $HOME).

* Web frameworks supporting HTTP sessions often use local storage for
  session data.  This will not work over multiple servers, for the same
  reason as local files.  To fix this, configure your framework to store
  session data in $HOME or a MySQL database instead of local files.
  (No changes are needed for PHP, which is already configured this way.)

* Tools which expect server-specific details (e.g. hostname or IP
  address) to remain the same will not work.  This is always a bad idea,
  but will now not work at all.

* Tools which require some kind of separate daemon will need to start
  the daemon on both systems, or communicate with the daemon over the
  network.

* Initially, there will be independent access and error logs for
  each system.  To ease debugging of scripts, it will be possible to use
  a URL like <http://wolfsbane.toolserver.org/~jsmith/mytool/> to force
  the request to a particular system.  However, such URLs should not be
  used for any other purpose, since server names can change at any time,
  which would break the URLs.

  In the future, we hope to have unified logs for all web servers.

We plan to have the additional web server operational within the next
week or two.

	- river.
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