ts - ticket sandboxes
=====================

ts parks a Redmine ticket as its own frozen browser instance on hgwdev.  You can
leave the ticket, work on something else, and return to it later.  You can also
give a reviewer a URL for it.  refs #37867

Only the code is frozen.  Each parked instance holds a full copy of your live
cgi-bin-$USER and htdocs-$USER, plus a rewritten hg.conf.  The MySQL databases,
/gbdb, and the browser trash stay shared with the live CGIs.  A private httpd,
running as you, serves the copy on a loopback high port.  It needs no root, no
DNS, and no vhost.

The one thing ts does not share is the udc cache.  Each ticket gets its own
directory under the shared trash, trash/udcCache/ts/NNNNN.  See Notes.

Two files:

  ts       the real tool.  Runs on hgwdev.
  ts.mac   a thin wrapper for your laptop.  It runs ts subcommands over ssh and
           opens the local ssh -L tunnel.  Install it as "ts" on the laptop.

Setup on hgwdev.  A freeze uses a few gigabytes per ticket, so keep the parked
instances on a large local pool instead of your home directory:

  mkdir -p /data/home/$USER/ticketSandboxes
  ln -s /data/home/$USER/ticketSandboxes ~/ticketSandboxes

Set TS_ROOT if you want them somewhere else.  Run "ts" with no arguments for the
subcommand list.

Typical use:

  ts create 37867 "some note"     freeze the live sandbox and start the httpd
  ts sync 37867                   re-freeze after more work on the live sandbox
  ts conf 37867                   rewrite the config only, keeping the freeze
  ts list                         show every parked ticket and its status
  ts tunnel 37867                 open the tunnel and print the browser URL
  ts remove 37867                 stop the httpd and delete the instance

Any hgwdev account can reach a parked instance, because all hgwdev users share
the machine's loopback:

  ssh -N -L PORT:localhost:PORT you@hgwdev.gi.ucsc.edu
  # then open http://localhost:PORT/cgi-bin/hgTracks

There is no password on a parked instance.  It shows only what any hgwdev user
can already build and query.

Notes
-----

The freeze is a full copy, not hardlinks.  Hardlinks only freeze a file against
replacement by rename, so an in-place edit of a live file would also change the
parked copy.

The CGIs read two htdocs directories.  The frozen htdocs-$USER is the
DocumentRoot, and the code also reads a sibling ../htdocs for files such as the
URW fonts.  Each parked instance keeps a symlink to the shared
/usr/local/apache/htdocs for that reason.  Without it, rendering fails because
it cannot find a font file.

udc caches remote bigData files by URL.  The live sandbox and every parked
ticket would otherwise read and write the same trash/udcCache tree, so a cache
entry written by one instance is read by all of them.  That breaks the freeze: a
sparse or bad entry written by one build reappears under another.  ts gives each
ticket its own trash/udcCache/ts/NNNNN instead.  It still lives in the shared
trash, so the trash cleaner ages it out like any other udc cache, and it is
still data: "ts sync" does not clear it.  "ts remove" does delete it.

"ts conf" adds this setting to an instance frozen before ts had it, so you do
not have to re-freeze to get a private cache.

Each instance draws its ticket number faintly across the page background, so you
always know which frozen browser you are viewing.  ts writes that stylesheet
into the frozen htdocs and sets browser.style in the frozen hg.conf.

ts does not replace the tip/beta/rel Docker instances.  Those reproduce an exact
released environment, including the database.

Write-up: https://hgwdev.gi.ucsc.edu/~braney/per-rm-sandboxes.html
