[mapserver-users] Parametrizing a MapCache config file

[David Hoese]

Hi,

I had a similar need where I was running MapCache in a docker container 
and needed the config to change based on some user-provided environment 
variables. I ended up writing a python script that uses the Jinja 
templating language. That way I could write a really complex config 
"template" and run my python script when the docker container started 
and produce the desired output config. It was extra nice for me because 
my jinja template allowed me to do "for" loops and in my case I had a 
lot of the same grids and tilesets that were only different by one or 
two parameters.

It would be nice if there was something builtin, but I think a sed 
script or something like my Jinja templating are the easiest solutions.

Dave

Example
-------

     <!--    Overlays -->
     <source name="{{ plat }}_{{ inst }}_borders" type="wms">
         <getmap>
             <params>
                 <FORMAT>rgba</FORMAT>
                 <LAYERS>bw_map</LAYERS>
             </params>
         </getmap>
         <http>
             <url>http://{{ wms_host }}:{{ wms_port }}/wms/borders</url>
             <connection_timeout>10</connection_timeout>
             <timeout>15</timeout>
         </http>
     </source>

Python (trimmed down)
---------------------

     tmpl_vars = {'wms_host': 'my_host', 'wms_port': 8888, 'plat': 
'test', 'inst': 'example'}
     with open(args.template_fn, 'r') as tmpl_file:
         template = jinja2.Template(tmpl_file.read())
         print(template.render(tmpl_vars))

I then run it like:

python render.py > /path/to/output_config.xml

On 12/17/20 7:26 AM, Schmid Andreas wrote:
> Hi list
> 
> I'm looking for a way how I could parametrize a MapCache XML config file. Up to now, I have three config files: One that I use for development purposes, one for running MapCache in the test environment, and one for the production environment. The files differ only in the URL of the service metadata, the URL of the http-source, and whether the demo service is enabled. So when I change something in the file, I always need to make sure that I make the same change in the other files. Which I don't really like because it's error-prone.
> 
> One solution that I can think of is keeping only one file and putting placeholders in the appropriate places. And then running a sed-Script over it before deploying it.
> 
> But maybe someone knows of a smarter idea for this?
> 
> Thanks a lot,
> Andy
> 
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