QWC QGS Cache Pre-Seed

Docker image for pre-seeding the QGIS Server QGS project cache.

This image will periodically query the capabilities for all/selected QGS projects below the projects directory to ensure that the projects are cached in the QGIS Server project cache, helping to avoid slow server responses which occur when a project is not in cache.

Setup

Add the qwc-qgs-cache-preseed container configuration to your QWC docker-compose.yml:

  qwc-qgis-server:
    image: docker.io/sourcepole/qwc-qgis-server:<tag>
    environment:
      FCGI_MIN_PROCESSES: 10
      FCGI_MAX_PROCESSES: 10
      ...
    volumes:
      - ./volumes/qgs-resources:/data:ro
      ...
      
  qwc-qgs-cache-preseed:
    image: docker.io/sourcepole/qwc-qgs-cache-preseed:<tag>
    environment:
      EXECUTE_ON_STARTUP: 1
      CRON_SCHEDULE: "0 3 * * *"
      QGS_EXT: ".qgs"
      FCGI_INSTANCES: 10
    volumes:
      - ./volumes/preseed_services.txt:/preseed_services.txt:ro
      # OR
      # - ./volumes/qgs-resources:/data:ro
      # OR
      # - ./pg_service.conf:/srv/pg_service.conf:ro

Configuration

To control which QGS projects will be processed, you can:

• Mount a file to /preseed_services.txt which contains the services names, one per line. For example:
  • subdir/projectname for a QGS file located in qgs-resources/subdir/projectname.qgs
  • pg/schema/projectname for a QGS project located in a DB in schema schema and named projectname
• Mount the qgs-resources dir (or whichever directory is mounted to /data for qwc-qgis-server) to /data, which will be then searches for projects (ending with $QGS_EXT).
• Mount a postgres service configuration file to /srv/pg_service.conf. The service file should contain a [qgisprojects] service definition. It would consider all projects located in the service DB in a specific schema. The ENV PG_DB_SCHEMA can be used to set the schema name (defaults to qwc_config).

The following environment variables can be set:

Name	Default	Description
CRON_SCHEDULE	0 3 * * *	Interval at which the pre-seeding script is run. Default: every day at 03:00.
EXECUTE_ON_STARTUP	0	Whether to run the script when the container starts.
QGS_EXT	.qgs	The QGS project extension to look for (.qgs or .qgz).
FCGI_INSTANCES	10	The number of FCGI instances (i.e. the number if simultaneous requests to send).
SLEEP_INTERVAL	1	The sleep interval in seconds between sending requests.
DEFAULT_QGIS_SERVER_URL	http://qwc-qgis-server/ows/	The default URL of the QGIS server to send requests to.
PG_DB_SCHEMA	qwc_config	The name of the DB schema which stores QGIS projects in a table qgis_projects.

Note: You should set FCGI_MIN_PROCESSES equals to FCGI_MAX_PROCESSES in the qwc-qgis-server container configuration and FCGI_INSTANCES to the same number in the qwc-qgs-cache-preseed container configuration.