Pre-filling disk storage

One of the popular features of Athens is that it can be run completely cut off from the internet. In this case, though, it can’t reach out to an upstream (e.g. a VCS or another module proxy) to fetch modules that it doesn’t have in storage. So, we need to manually fill up the disk partition that Athens uses with the dependencies that we need.

This document will guide you through packaging up a single module called github.com/my/module, and inserting it into the Athens disk storage.

First, get the tools

You’ll need to produce the following assets from module source code:

  • source.zip - just the Go source code, packaged in a zip file
  • go.mod - just the go.mod file from the module
  • $VERSION.info - metadata about the module

The source.zip file has a specific directory structure and the $VERSION.info has a JSON structure, both of which you’ll need to get right in order for Athens to serve up the right dependency formats that the Go toolchain will accept.

We don’t recommend that you create these assets yourself. Instead, use pacmod

To install the pacmod tool, run go get like this:

$ go get github.com/plexsystems/pacmod

This command will install the pacmod binary to your $GOPATH/bin/pacmod directory, so make sure that is in your $PATH.

Next, run pacmod to create assets

After you have pacmod, you’ll need the module source code that you want to package. Before you run the command, set the VERSION variable in your environment to the version of the module you want to generate assets for.

Below is an example for how to configure it.

$ export VERSION="v1.0.0

Note: make sure your VERSION variable starts with a v

Next, navigate to the top-level directory of the module source code, and run pacmod like this:

$ pacmod pack $VERSION .

Once this command is done, you’ll notice three new files in the same same directory you ran the command from:

  • go.mod
  • $VERSION.info
  • $VERSION.zip

Next, move assets into Athens storage directory

Now that you have assets built, you need to move them into the location of the Athens disk storage. In the below commands, we’ll assume $STORAGE_ROOT is the environment variable that points to the top-level directory that Athens uses for its on-disk.

If you set up Athens with the $ATHENS_DISK_STORAGE_ROOT environment variable, the root of this storage location is the value of this environment variable. Use export STORAGE_ROOT=$ATHENS_DISK_STORAGE_ROOT to prepare your environment for the below commands.

First create the subdirectory into which you’ll move the assets you created:

$ mkdir -p $STORAGE_ROOT/github.com/my/module/$VERSION

Finally, make sure that you’re still in the module source repository root directory (the same as you were in when you ran the pacmod command), and move your three new files into the new directory you just created:

$ mv go.mod $STORAGE_ROOT/github.com/my/module/$VERSION/go.mod
$ mv $VERSION.info $STORAGE_ROOT/github.com/my/module/$VERSION/$VERSION.info
$ mv $VERSION.zip $STORAGE_ROOT/github.com/my/module/$VERSION/source.zip

Note that we’ve changed the name of the .zip file

Finally, test your setup

At this point, your Athens server should have its disk-based cache filled with the github.com/my/module module at version $VERSION. Next time you request this module, Athens will find it in its disk storage and will not try to fetch it from an upstream source.

You can quickly test this behavior by running below curl command, assuming your Athens server is running on http://localhost:3000 and is already configured to use the same disk storage that you pre-filled above.

$ curl localhost:3000/github.com/my/module/@v/$VERSION.info

When you run this command, Athens should immediately return, without contacting any other network services.

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