gemini-hlsw / lucuma-itc   0.21.5

Scala versions: 3.x
Scala.js versions: 1.x


This is a graphql server acting as a proxy for the old ocs2-based itc server


It is possible to run locally using sbt

   sbt ~service/reStart

When using sbtn there is no output (see spray/sbt-revolver#99).

Note, it is important to have git lfs installed in order to obtain the necessary classes for running the ITC. See (git lfs and Legacy ITC Code below).

You can then open the playground to work with the API by pointing your browser to



The app needs an environment variable, REDISCLOUD_URL, which points to the redis server used for caching. For example: REDISCLOUD_URL = "redis://localhost".


ITC calculations are relatively expensive and they are pure (a given input always produces the same output) the lucuma ITC server uses redis to store the results linking them from the request parameters to the results

The cache design is optimized to use minimal space given some of the responses (graphs) are fairly large. We are also assuming we'll never need to go inside the cached data to edit the data and we can discard items at any moment.

The keys are stored as itc:prefix:hash where hash is just the hash of the parameters

A few diferent encodings were tested to reduce size. Here are some measurement

  • Plain json: 1441864
  • Compressed json: 589896
  • Boopickle: 262216

Cache flushing

The only reason for the remote values to be stale is if the old itc changes (happens not very often) lucuma-itc will check on startup and verify if the itc data has changed. If so it will flush the whole cache

git lfs and Legacy ITC Code

The itc calculations are mostly done in java and scala using legacy technologies, in particular libraries like scala 2.11, scalaz, argonaut. We were wrapping this code in an http server but that incurred considerable overhead especially when the graph data was needed. As an alternative we can now directly call the java code but given the use of legacy libraries this requires the jar files to be loaded dynamically by the application and be called via reflection with a custom classloader

In case the code in ocs2 changes we need to update the jar files using the script. The jar files are fairly large (they contain the data files used to calculate the itc results). Given github limitations these need to be stored in git lfs.

Install git lfs to get the necessary jar files.

Long term

Ideally we'd port the old ITC codebase and integrate it here. This is no small task but an initial attempt was started on the legacy-port branch


This project needs the following buildpacks to be used in heroku (order is important)

=== itc-master Buildpack URLs
2. heroku/scala

First we need git lfs to get the files stored in github lfs Then scala to build the app And finally post-build-clean to reduce the slug size