# \[CI Caching\] Downloading project dependencies without building the app?
**URL:** https://discourse.elm-lang.org/t/ci-caching-downloading-project-dependencies-without-building-the-app/5140
**Category:** Learn
**Created:** [February 6, 2020, 4:26pm UTC](https://discourse.elm-lang.org/t/ci-caching-downloading-project-dependencies-without-building-the-app/5140 "2020-02-06T16:26:39Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Janiczek](https://discourse.elm-lang.org/u/Janiczek)
#### Post date: [February 6, 2020, 4:26pm UTC](https://discourse.elm-lang.org/t/ci-caching-downloading-project-dependencies-without-building-the-app/5140/1 "2020-02-06T16:26:39Z")
Hello! After the recent [package.elm-lang.org](http://package.elm-lang.org) situation we’re trying to cache the ELM\_HOME directory in Docker/Drone CI, to be more resilient to zipballs HTTP request outages and also to not do needless work in each CI build.
The problem we’re dealing with is: _we don’t want to trigger downloading packages on every application code change_ (`source_directories`).
The way Dockerfiles work makes us do:
- ADD elm.json
- ADD all the various source\_directories (we have a lot of them)
- RUN elm make some/File.elm --output /dev/null
which has the disadvantage mentioned above.
A workaround I can see is making temporary Elm files which the Dockerfile will then try to compile. Thus skipping the “ADD source directories” step.
But it seems to me something like `elm make --install-only` or `elm-json download` (cc @ilias) would be more correct solution.
Do you see a different solution?
---
### Author:  [@ilias](https://discourse.elm-lang.org/u/ilias)
#### Post date: [February 6, 2020, 5:04pm UTC](https://discourse.elm-lang.org/t/ci-caching-downloading-project-dependencies-without-building-the-app/5140/2 "2020-02-06T17:04:26Z")
Running `elm make` without arguments is basically an `--install-only` command.
Caveats:
- the source-directories must exists, however, they don’t have to have anything in them. So if you can get away with something like `mkdir -p foo bar/baz`, that would be an easy solution!
- it exits with `1` so it’s hard to distinguish from “actual” failure
---
### Author:  [@Janiczek](https://discourse.elm-lang.org/u/Janiczek)
#### Post date: [February 7, 2020, 9:43am UTC](https://discourse.elm-lang.org/t/ci-caching-downloading-project-dependencies-without-building-the-app/5140/3 "2020-02-07T09:43:12Z")
At the moment, until a better solution arrives, we went with the hack:
```auto
# A hack to be able to download dependencies without compiling our source code
# ------
# We want to avoid `COPY ./client /pro/client` before the `elm make` above all costs.
# That would download the dependencies on every code change...
# ------
# Plan:
# * `mkdir -p` the source directories
# * create a dummy Elm module in one of them
# * compile that one
COPY elm.json /pro/elm.json
RUN mkdir -p \
client/_factories \
client/_share/src \
client/app-monolithic/src \
client/audience-builder \
client/chart-builder/src \
client/crosstab-builder/src \
client/dashboards/src \
client/elm-dashboards/src \
client/fullscreen-search \
client/products/src \
client/settings/src \
client/tv-study/src
RUN echo "module DummyMain exposing (..)\nx = 1" >client/app-monolithic/src/DummyMain.elm
RUN elm make ./client/app-monolithic/src/DummyMain.elm --output /dev/null
# ^ Now we have downloaded the dependencies in a layer that's before adding the source code!
# That means dependencies will only download when elm.json changes, not when the source directories change.
RUN rm -rf ./client/app-monolithic/src/DummyMain.elm
# Sometime later: COPY ./client /pro/client
```
---
### Author:  [@choonkeat](https://discourse.elm-lang.org/u/choonkeat)
#### Post date: [February 12, 2020, 4:44am UTC](https://discourse.elm-lang.org/t/ci-caching-downloading-project-dependencies-without-building-the-app/5140/4 "2020-02-12T04:44:00Z")
Adapted from your code, I made [a pair of `Dockerfile` and `Makefile`](https://gist.github.com/choonkeat/d40462479dce88182a7ac8c5bd87f2c4) that is cache friendly (only injecting `elm.json` and `Dockerfile` itself for the build) and can be applied to individual projects. As long as it’s run against the same docker server, the layers should cache automatically.
```auto
make elm-stuff/.elm
```
then subsequently, CI commands just need to have env `ELM_HOME=elm-stuff/.elm` set
e.g.
```auto
export ELM_HOME=elm-stuff/.elm
elm-test
elm make src/Main.elm
```
---
### Author:  [@turboMaCk](https://discourse.elm-lang.org/u/turboMaCk)
#### Post date: [February 12, 2020, 10:17am UTC](https://discourse.elm-lang.org/t/ci-caching-downloading-project-dependencies-without-building-the-app/5140/5 "2020-02-12T10:17:13Z")
While I think work around like this can work for most of the people there are some additional things you might be interested in.
- `ELM_HOME` environment variable can be used to define location of elm cache
- Elm uses `registry.dat` binary which is a snapshot of packages.
- [This is how you can download package data without elm](https://github.com/NixOS/nixpkgs/blob/99f2e88123192fea040c46681d7497f1d0933db4/pkgs/development/compilers/elm/makeDotElm.nix)
- [This is how binary file is generated](https://github.com/cachix/elm2nix/blob/38b61e45a860d7512f2ec2e458cf01c688835ddf/src/Elm2Nix/PackagesSnapshot.hs)
---
### Author:  [@system](https://discourse.elm-lang.org/u/system)
#### Post date: [February 22, 2020, 10:17am UTC](https://discourse.elm-lang.org/t/ci-caching-downloading-project-dependencies-without-building-the-app/5140/6 "2020-02-22T10:17:18Z")
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