Thumbnail generator for Election Leaflets

This is a Lambda function that produces thumbnails from raw leaflets and puts the resulting files in a deterministic structure for compatibility with sorl-thumbnail.

It uses sorl-thumbnail under the hood and accepts the same options as the thumbnail templatetag. Output files are named as follows:

/thumbs/{size}/{optkey1}={optval1}/{optkey2}={optval2}/.../path/to/file.jpg

Example:

https://data.electionleaflets.org/thumbs/600/crop%3Dcenter/leaflets/2019-11-26_1.jpg

The Lambda function can consume either CloudFront or S3 events, so it can be used as new leaflets are uploaded, or to backfill thumbnail URLs as they're requested.

Configuration

The pre-emptive processing of thumbnails from S3 events needs configuration for the thumbnail specs we want to create. This is done in the SPECS constant in the handle_s3 function in src/handler.py, which expects a tuple of tuples. The first element is the size spec, e.g 600 or 300x400. The second element is the options dict, eg {"crop": "top", "upscale": True}.

Deployment

❗ Currently must be built from a Linux machine, Docker support coming soon for Macs ❗

Deployment is a four-stage process, covering S3 and CloudFront. You must have a Democracy Club AWS profile active.

1. Run make deploy_cf
2. Note the FunctionArn returned and update it in the thumbs/* behaviour in the data.electionleaflets.org CloudFront distribution. This will take 10-15 minutes to update.
3. Run make deploy_s3
4. Note the FunctionArn returned and update it in the Events -> el-resize-image property for the data.electionleaflets.org S3 bucket