# SEDModS -- VLKB SED Models web service

This service is meant to provide filtering on top of the SED Models
(big, 30M rows) catalogue table. The table was initially served as a
RDBMS table and queried through SQL directly.

This work moves it onto a python+HDF5 solution.

The service is deployed as a python+WSGI on httpd, within a podman
container to help maintenance.

## Deploy SEDModS

### Pull repo
When pulling this repo you'll end up with

    |-- Dockerfile (container description)
    |-- README.md (this text)
    |-- sed-data
    |   `-- link.to.hdf5 (dummy data file, see later)
    |-- wsgi.conf (WSGI configuration for the http server)
    `-- wsgi-scripts (actual service business logic)
        |-- hdf_query.py
        |-- query-server_d.py
        |-- wsgid.py
        `-- wsgi.py

### Project content description
The `Dockerfile` cotains instructions to build the container that
includes:
 - an httpd server (running on container's port 80)
 - python and WSGI packages to be able to run the service
It needs a properly configured `wsgi.conf` that will be loaded within
the `http/conf.d` of the container.
The base container is a _fedora:latest_ environment.

Besides the instructions to build the container and the WSGI
configuration, the container, to properly run, needs two further pieces,
two folders:
 - the `sed-data` one that contains the SED Models HDF5 file
 - the `wsgi-scripts` that actually contains the business logic of the
   service itself

(The actual HDF5 file is not kept in this repo, because it's too large
and because it's not a wise choice to store byte-blobs in a versioning
system).

The `wsgi-scripts` is provided and maintained in this repo, the
`sed-data` one can be anywhere else, in reach of the host system.
If the location of these these pieces has to be changed, it suffices to
update accordingly the run command of the container (see below).

### Build the container image
To build the container image, simply run 

    podman build --tag vlkb-sedmods -f ./Dockerfile

The tag can be one of your choice. It is suggested to have a dedicated
user to run this in production.

### Run the container
Once the podman image is ready and the two directories are in place, to
run the container it suffices a command like

    podman run -dt \
        --name sedmod-test \
        --rm \
        -v $PWD/sed-data:/sed-data:z \
        -v $PWD/wsgi-scripts:/var/www/wsgi-scripts:z \
        -p 8080:80 vlkb-sedmods

where the name is optional and of your choice and the left-hand side of
the _:_ in the _-v_ arguments must point to the actual location of the
two folders to be mounted in the container.

In the example the _-v_ arguments are considered such as the command is
run from the local working copy and the HDF5 SED Models file is actually
within the `sed-data` folder.

Also, _-p_ maps the 80 port of the container onto the 8080 port on the
host server, this must be changed if the host's 8080 is already in use.

### Service(s) in the container

Two flavours of the _SEDModS_ service can run with the repo content:
 - one that reads the HDF5 at each query
 - one that reads the HDF5 once and works as a _system daemon_

#### Single query service mode
This mode is directly available when the cotainer is run. It uses the
following code files:

    wsgi.py
    hdf_query.py

If you run on the host server 

    curl localhost:8080/sedsearch/?'clump_mass<10.005' > output.dat

you should get the response in the `output.dat` file, or you can point
the browser to

    http://host.server:8080/sedsearch/?'clump_mass<10.005'

and see the response directly.

#### Daemon service mode
This mode uses the code in:

    wsgid.py
    query_server_d.py

It requires a couple of processes to run before the deamonised service
can work. These processes run within the container, so, after running
it, one can launch them attaching to the running container with

    podman exec -it sedmod-test /bin/bash

and within it run

    python -m Pyro4.naming &
		python query-server_d.py &

After that, on can exit the shell and the daemon-based service should be
reachable at

    http://host.server:8080/seddaemon

with the same usage of the single query one.

### Network Proxy
Since it could be annoying to explitly use port 8080 on the host, the
service can be made visible on a specific context path in the host
server's http using the httpd _ProxyPass_ directive, like
  
    <Location "/sedmods">
        ProxyPass "http://localhost:8080"
    </Location>

where _/sedmods_ is an example and the _8080_ port depends on the passed
parameters to the podman run command (see above).

## SED Models HDF5 file
This is preserved, currently, on the INAF ICT Owncloud instance.

## Dependencies

On the host:
 - podman
 - httpd

Within the container (i.e. provided in the build):
 - httpd with python3-mod\_wsgi
 - python 3.x
 - pandas
 - Pyro4 (deamon mode)
 - (py)tables