Unicorn is a forking server with the idea that master process preloads
heavy Ruby-on-Rails application, and then to handle new request a worker
process is forked with application already loaded in its memory (and
modification being tracked by OS via copy-on-write).

From this point of view the only reasonable value for preload_app is
always "true" and omnibus-gitlab does this:

    https://gitlab.com/gitlab-org/omnibus-gitlab/blob/8eda0933/files/gitlab-cookbooks/gitlab/definitions/unicorn_service.rb#L65

Then unicorn documentation shows what code has to be there in pre-/post-
forking event:

    http://bogomips.org/unicorn.git/tree/examples/unicorn.conf.rb?id=3312aca8#n57

GitLab uses only part of it that "allows a new master process to
incrementally phase out the old master process with SIGTTOU to avoid a
thundering herd":

    https://gitlab.com/gitlab-org/omnibus-gitlab/blob/8eda0933/files/gitlab-cookbooks/gitlab/definitions/unicorn_service.rb#L69
    http://bogomips.org/unicorn.git/tree/examples/unicorn.conf.rb?id=3312aca8#n75

but strangely does not use code parts that are "highly recommended" or
"require" for "Rails + "preload_app true"" case.

For the reference I've added such codes, but kept them being commented
out.

/cc @kazuhiko, @jerome

Convert unicorn parameters to slapos and configure it to listen on unix
socket only.

( Omnibus configures unicorn to listen on unix socket and
  loopback TCP, mainly because gitlab-shell could not connect to unicorn
  via unix socket until recently:

      https://gitlab.com/gitlab-org/gitlab-shell/commit/184385ac

  But as it can now, there is no point to keep on TCP port open )

To be able to do such configuration we add stub to unicorn service
section (to create needed directories where to keep the socket).

There will be follow-up patch which configures unicorn pre/post-forking
actions, which is not trivial and thus better be done on its own.

/cc @kazuhiko, @jerome

Convert the rest of this configuration file to slapos.

It is straightforward conversion of parameters except:

    - access-via-ssh is disabled (gitlab slapos version does not support
      ssh access and supports HTTP(S) only by design on purpose)

    - we do not support restricting possible projects visibility via
      instance parameter (very low chance this will be needed in
      practice)

    - default issue-closing pattern is just ok for now and not
      configurable

    - support for builds, build artifacts & CI is disabled (we do not
      support CI (yet ?))

    - some internal defaults are just ok (e.g. where to organize
      directory for keeping repositories archives for downloads)

    - reply-by-email is not supported (yet ?)

    - we do not support LFS (yet ?) - just plain git hosting is ok for now.

    - Gravatar defaults are ok for now and not configurable.

    - Support for LDAP is disabled

    - Support for Kerberos is disabled

    - Support for OmniAuth is disabled

    - Satellites path is just /dev/null as we start from version where
      satellites are already non-existent.

    - Uploading backups to somewhere via GitLab's builtin mechanism is
      not supported - we'll use SlapOS native backup and resiliency for
      this.

    - Support for Google analytics is disabled.

    - Support for Piwik is disabled.

    - we are ok (for now) with default rack-attack git settings

/cc @kazuhiko, @jerome

This user will need to be specified several times in configuration
files, as by default gitlab uses 'git' user and does "sudo" to it if it
is not current.

We will use {{ backend_info.user }} in the upcoming patches.

/cc @kazuhiko, @jerome

GitLab has a notion of "external URL" - the canonical "frontend" URL the
server is reachable through: this URL is used as prefix to show
e.g. git-clone URL for repositories, etc, even if a server can be
reachable via several frontends.

Add external_url handling to slapos instance.

NOTE whether to use https or not is also defined by external_url, in
particular by external_url scheme.

/cc @kazuhiko, @jerome

Convert to slapos SMTP settings for gitlab:

    - convert to jinja2
    - remove support for gitlab CI (we do not support it (yet ?))
    - add handling of `smtp_enable` parameter directly to that file
      ( omnibus handles this parameter externally and just removes
        smtp_settings.rb if it is true )

NOTE smtp_settings.rb contains SMTP password, so it is mode is set to 0600.

/cc @kazuhiko, @jerome

Just another 2 simple parameters (attack detection tunables) conversion
to jinja2/slapos.

/cc @kazuhiko, @jerome

Just convert 2 parameters used in that file to jinja syntax and add
those parameters (unicorn OOM killer tunables) to gitlab-parameters.cfg

/cc @kazuhiko, @jerome

A simple change just to point resque to redis unix socket.

/cc @kazuhiko, @jerome

We tweak database.yml to point to our postgresql unix socket; set
adapter to hardcoded postgresql, encoding to unicode and omit collation
(which according to omnibus-gitlab is used for mysql only).

The only instance parameter imported from omnibus is `db_pool` - how
many connection to a DB to keep open in a RoR thread/process.

XXX we use db's superuser as a user to connect. Is it ok to do even if
    the whole DB is used only for gitlab? (I think it is ok for the
    first iteration, but we'll probably need to refine this later)

/cc @kazuhiko, @jerome

Introduce a library of Jinja2 macros that will be handy to use in
templates. For now we add only 2 macros:

    cfg(name)   - to get instance configuration parameter `name`,   and
    cfg_bool    - to get truth value of ----//----

The reason we introduce cfg() is that we will need to use a lot of
parameters in many places and it is much more handy to write, e.g.

    cfg('email_enabled')

compared to

    instance_parameter:configuration.email_enabled

/cc @kazuhiko, @jerome

We will be using a several dozens of parameters to control gitlab
instance. It makes sense not to deviate in such parameters namings and
defaults from omnibus version.

Thus for such parameters - for clarity - we organize a separate file
where we will be keeping them - gitlab-parameters.cfg.

In this patch series all used parameters will be "imported" from
omnibus-gitlab 8.2.3+ce.0-0-g8eda093.

NOTE it is maybe better to try to autogenerate that file from upstream
    omnibus parameters definitions. If time will tell it becomes hard to
    maintain our copy - we'll consider going that way.

/cc @kazuhiko, @jerome

- Download them on SR build and pass info to instance
- Instance prepares to process them as jinja2 templates
- Instance hooks the files into configuration location as appropriate

Every file so far is renamed *.erb -> *.in and a header added showing
that this file is autogenerated with links about what was the base
gitlab and/or omnibus version and omnibus reference revision this
template was last updated for.

So far all result configuration files are invalid - because ERB syntax
is there. We will convert the configuration files to proper jinja2
syntax and to using slapos parameters incrementally in the upcoming
patches.

NOTE (again): md5 sums are not yet fixed - we will fix them in the end
    of gitlab patches series after applying all tweaking changes.

/cc @kazuhiko, @jerome

Pristine import of template configuration files from omnibus GitLab
package. All files were imported as-is in their ERB form and filenames
from omnibus-gitlab 8.2.3+ce.0-0-g8eda093 from here:

    https://gitlab.com/gitlab-org/omnibus-gitlab/tree/8eda093/files/gitlab-cookbooks/gitlab/templates/default

We will convert the templates to jinja2 and adjust them to slapos
version in the following patches.

Scheme for synchronizing with future upstream changes is envisioned as this:

    - checkout latest commit which updated pristine erb files
    - copy updated files from omnibus-gitlab, and commit the updates
    - checkout slapos master
    - merge commit that updated erb

That should reasonably work with not too-many conflicts and even those
should be not hard to resolve (with `git mergetool` e.g. in kdiff3)

/cc @kazuhiko, @jerome

Organize per-instance place for gitlab configuration and work directory.

Unfortunately as GitLab is Ruby-on-Rails application, it is not possible
to keep its code in one place and have multiple separate configuration
sets in different places and start that code for a configuration set -
GitLab and Rails insist to get configuration from relative to source
code tree.

GitLab omnibus "solves" this by having only one configuration set and
having symlinks from code to that only configiration set. In slapos we
can potentially have several instances for one software and thus we
cannot do that.

With such limitations a proper solution would be to bind-mount software
code into instance filesystem namespace close to configuration - that
way the code will be only one and will find proper per-instance config.
Currently we do not have namespaces available on slapos unfortunately,
thus something else is needed.

The workaround I decided to do is this: to clone cloned gitlab
repository from software/ space to instance/ space and adjust it in
instance space. This has the following drawbacks:

    - code is duplicated
    - code becomes read-write, instead of being read-only

but imho it is the most practical thing to do. Another solution could be
to patch GitLab / Rails to remove "config lives in code" assumption, but
the number of places where this needs to be done is really many.

NOTE gems which gitlab uses and which were installed during software
    compilation are not duplicated - they are reused via bundler - via
    pointing BUNDLE_GEMFILE to original location in software.

NOTE2 For instance tasks and also for maintanace convenience we establish
    <instance>/bin/gitlab-* programs, e.g. gitlab-rake, which e.g. for
    gitlab-rake will run rake with correctly loaded gitlab environment -
    like in gitlab-omnibus.

/cc @kazuhiko, @jerome, @jp

Organize internal Redis service, like with PostgreSQL in the previous
patch, with the help of slapos.cookbook:redis.server recipe.

Like with postgresql, and as we planned, redis listens only on
internal-to-partition unix socket.

The recipe establishes both service and promise to check it is alive;
we only need to setup log rotation manually.

/cc @kazuhiko, @jerome

Organize internal PostgreSQL database which will be used as DB for
Roby-on-Rails GitLab and listens only on unix socket (for security and
performance reasons - see earlier intro patch).

To do it we use slapos.cookbook:postgres recipe, with disabling
"listen-to-network" via passing empty sets to ipv4 and ipv6 recipe
arguments.

The promise to check whether DB is alive is just `psql -c '\q'` which
will error if failing to connect to DB, but exit silently if connected ok.

Explicit log rotation is not needed - as postgresql logs to
stdout/stderr - not to a file - logs are handled by slapos - put into
.slappartX_postgresql.log and automatically rotated there.

XXX omnibus-gitlab tunes postgresql with shared_buffers and other
parameters, most likely for performance reasons - see e.g.

    https://gitlab.com/gitlab-org/omnibus-gitlab/blob/8-2-stable/files/gitlab-cookbooks/gitlab/templates/default/postgresql.conf.erb#L113

I decided not to fine-tune postgresql for now, and get on-field feedback
first, and then, if needed, we can tune.

/cc @kazuhiko, @jerome

A recipe could do

    [promise-<service>]
    <= promise-wrapper
    command-line = ...

and the wrapper will be put automatiaclly into etc/promise/<service>.

( for this to happen !py! magic is used again, like we did for logrotate
  and cron entries before )

/cc @kazuhiko, @jerome

gitlab: Make a plan to base instance layout on gitlab-omnibus and to interconnect all internal services via unix sockets

Upcoming changes will follow two points:

- we try to base our gitlab setup on how it is done in
  gitlab-omnibus[1] with the idea to ease tracking upstream changes to
  instance setup.

- we will interconnect all internal services via unix sockets only.

  The reason to do it is twofold:

    1. easier security: currently files on different slapos partitions
       are isolated from each other, but there is no "in-between-partitions"
       networking isolation - thus (potentially evil) programs can
       access internal services on other slapos partition.

       permissions to access unix sockets, on the other hand, are
       managed by filesystem-level permissions, and thus unix sockets in
       one partition will be, by default, isolated from programs on
       another partitions.

    2. It is well known that UNIX sockets are faster than TCP over
       loopback. For example for our std shuttles they have 2 times lower
       latency and ~ 2-3 times more throughput compared to TCP over loopback

    More details on 1 & 2 can be found e.g. here:

    nexedi/slapos!27
    https://gitlab.com/gitlab-org/gitlab-shell/merge_requests/30

/cc @kazuhiko, @jerome

[1] https://gitlab.com/gitlab-org/omnibus-gitlab

Add stub instance configuration which just establishes a way to have
several software types(*), pass all needed info from software to
instance, organizes base directory and establishes log rotation base for
upcoming services.

Log rotation is done with the help of cron periodicallly calling
logrotate. The rotation is done in "copytruncate" mode - i.e. log file
is not moved away and signal sent for service to reopen it, but instead
log content is just copied to outside and there is no need for a service
to reopen it's log file.

The reason it is done this way, is that there is a chance of not
handling such "reopen-log-file" callbacks correctly on a service side,
and so the net is full of crashing reports, e.g. like this:

    http://serverfault.com/questions/627521/why-is-logrotate-causing-apache-to-seg-fault-each-time

That's why we take a safer approach instead, even if "copytruncate" mode
is risking to loose several log entries(**) on rotation.

NOTE services will organize log rotation with just

    [logrotate-entry-<service>]
    <= logrotate-entry
    log     = path/to/log/files/*.log

For this to work some "!py!" magic (our way to serialize object into
executable python and process it in buildout recipes) is used to process
section names.

The approach trick is also used for cron, e.g. logrotate registers to
cron this way:

    [cron-entry-logrotate]
    <= cron-entry
    time    = daily
    command = ${logrotate:wrapper}

NOTE2 instance md5 are not fixed yet - we'll fix them after applying all
    patches in gitlab series.

(*) for now there is only 1 - "gitlab", but we'll need to have "-export"
    and "-import" for resiliency in the future.

(**) ideally such things should be done with logfs - a filesystem
    specializeing in logging - for client services it will look like as
    they just continue to write to log file, and on log service side, the
    rotation can happen, all transparent to client service.

/cc @kazuhiko, @jerome

First step - build all needed software. We build:

- Git
- PostgreSQL 9.2
- Redis 2.8
- Nginx

- gitlab-shell
- gitlab-workhorse
- gitlab-ce 8.2 itself

and everything which is needed to build the above programs.

Git is needed because GitLab is a git-hosting service and uses git
underneath. PostgreSQL is used as DB by gitlab and Redis as a cache.

GitLab-shell is a small project to manage ssh access to the service
(we'll disable ssh though) and to perform all "change a repository"
operations.

GitLab-workhorse is a service which offloads long-running or slow
request from main GitLab service.

GitLab-ce is the main Ruby-on-Rails-based web application.

Ruby- and Go- based programs are built in a way similar to:

    - 31a45a94    (helloworld & helloweb: Ruby version), and
    - 24e82414    (helloworld & helloweb: Go version)

Version of all components, except Git, were picked the same, as used by
gitlab omnibus v8.2 .

/cc @kazuhiko, @jerome

Some dists like SLE_12 don't seem to have it.

../../stack/slapos.cfg is removed from component/*/buildout.cfg
because we normally don't specify it in component/
The OBS package will need to extend it.

Pin versions required for ipython==4.0.0 with ipykernel separated
from ipython eggs.
The split was in accordance to : https://blog.jupyter.org/2015/04/15/the-big-split/

/reviewed-by @kirr  (on nexedi/slapos!33)

ipython_notebook SR hooked with ERP5 kernel.
This kernel helps in interaction between erp5 and Jupyter frontend.
The patches have been cleaned up

Features:

- All the code execution is being done at erp5 side, Jupyter just acts as dumb client.
- Receives result as string and its mime_type and thanks to kernel, displays it accordingly.
- Interactions b/w erp5 and Jupyter frontend are based on HTTP requests.

Major changes:

- Addition of erp5 kernel
- Improvement in code according to guidelines(name, section name)
- Use jinja template as instance file and make it more dynamic
- Debugging added for ipython_notebook service.

Note: The certificate authentication changed has been reverted to the previous
one(done by creating wrapper around openssl command) for now.

/cc @Tyagov
/reviewed-by @kirr, @jerome  (on nexedi/slapos!33)

@jerome added --matplotlib=inline in 48eefab5 (ipython notebook) but it is
really neither needed:

   @jerome
   I remember adding this --matplotlib=inline line, but I am not sure it was
   ever needed. Using magic %matplotlib in notebook should be enough.

   @tiwariayush
   Yeah, for inline matplotlib in default python kernel, magics do there
   work(therefore neither pylab nor matplotlib alias are needed while starting the
   server), so I'd say leave this commit as it is and regarding version updation:
   a new patch making change wherever required.

nor supported:

   $ cat .slappart0_ipython_notebook.log
   [W 15:51:35.454 NotebookApp] Unrecognized alias: '--matplotlib=inline', it will probably have no effect.

Remove it.

P.S.

'--logfile' isn't available for ipython version 3.2.0 but we are not removing
it since we are planning to upgrade IPython to versions 4.x where it is supported.

Based on patch by @tiwariayush  (see nexedi/slapos!33)

Jupyter: Change section name to instance-jupyter so as not to raise conflict in case of multiple extends

/reviewed-by @kirr  (on nexedi/slapos!33)

Maintain consistency with the slapOS SR format.
This SR can be hooked with other SR(ex:wendelin) and its better
to follow one way of publishing result parameters

[ kirr: This essentially changes publication format to JSON:

    $ xslapos proxy show --params

    # before
    slappart0: ipython_notebook (type default)
        url = https://[2001:67c:1254:e:49::952d]:8888
        monitor_url = https://[2001:67c:1254:e:49::952d]:9685

    # after
    slappart0: ipython_notebook (type default)
        _ = {"url": "https://[2001:67c:1254:e:49::952d]:8888", "monitor_url": "https://[2001:67c:1254:e:49::952d]:9685"}

  I'm not convinced we really need this, nor that the .serialized version is
  the most oftenly used one:

    slapos$ git grep 'slapos.cookbook:publish$' |wc -l
    59
    slapos$ git grep 'slapos.cookbook:publish.serialised$' |wc -l
    13

  but we can have it and see how it goes, reverting if needed ]

/cc @jerome
/proposed-for-review-on nexedi/slapos!33

This helps in logging up the requests made by ipython_notebook service

[ kirr: To be clear - until log-level is set to DEBUG, IPython notebook does
  not log HTTP requests, and since logging of HTTP requests is considered normal
  for most of our services (Zope, Apache, etc), it makes sense to enable such
  functionality for notebook too.

  There is not much additional noise produced by --log-level=DEBUG - in
  practice ipython only prints what config files it uses on startup, so this
  should be ok to go. ]

/reviewed-by @kirr, @jerome  (on nexedi/slapos!33)

ERP5 kernel basic info/workflow:

1. User enters code on notebook cell and executes
2. Code is sent to kernel via websockets
3. Kernel sends request to ERP5
4. Code is executed by ERP5 and the result is returned back via request.
5. Result is received and rendered on the notebook frontend.
6. Other message formats such as error and status are also conveyed by the Kernel.

[ kirr: in IPython notebook speak kernel is something that allows IPython
  notebook server side to talk to execution backend. ERP5 kernel is a thing that
  allows ipython notbook to talk to ERP5 (with help on-ERP5-server special bt5
  installed which accepts and executes commands).

  The bt5 to handle notebook calls on ERP5 side - erp5-data-notebook - is
  proposed to be merged into erp5.git on erp5!29 ]

/initially-reviewed-by @kirr, @Tyagov  (in a lot of places, last time on !33)

IPython Notebook: Explicitly add environment variable around wrapper and use ipython directory inside instance in env

[ kirr: By default IPython keeps configuration and other files location in
  ~/.ipython . What this patch does is organize explicit directory in instance
  tree to keep such files  ]

/reviewed-by @kirr  (on nexedi/slapos!33)

IPython Notebook: Add dynamic-template-base section for common jinja related file section and extend them with this section