Emulate EFS locally by mounting a local filesystem

[jeffgca]

Describe your idea/feature/enhancement

I have a lambda function that needs to store short-lived pieces of data, things like token keys for api access or the most-recently-sent notification to an api to prevent spamming users with repetitive messages. This data needs to persist beyond the lifetime of the lambda function.

As I was exploring how to implement this, I read that AWS had recently added support for EFS to lambda, and I wanted to test how that might work in my functions, using the efs filesystem to store data compared to alternatives such as DynamoDB

Proposal

sam local invoke -e ./events/twitch-webhook.json --filesystem=./efs-tmp/

Things to consider:

1. Will this require any updates to the SAM Spec?

It should not, this is a local invocation feature.

Additional Details

This is a limited feature that might not fill all customer needs; some customers might prefer to be able to access remote EFS file systems while running their function locally. In this use case simply having a filesystem available is enough. In the use case of running sam local start-api to exercise the app's api, the will need to mock out whatever filesystem they depend on locally.

[dacgray]

For reference - this is how we get around this issue - at least for start-api.

https://github.com/dacgray/sam-local-start-api-container-image-volume-mount

[benjaminfiliatrault]

Work Around

I personally compiled the entire BE using webpack. So the entry point of the lambda is ./dist/main.js

If I need to access file that should "act" like EFS mounting I create a global variable for my mounting point based on the environment the lambda is.

So on local, I put the file I need to access in my ./dist/efs

This way the mounting point on the lambda /VAR/TASK will contains the efs folder in my dist

It's a work around if you need to access files and test some processes on them locally.

It cannot work across multiple lambdas only on the one you uploaded files

[qvdk]

The work around of @benjaminfiliatrault works for the Java runtime too.

In this case, I added the files in src/main/resources/efs/.

Then, I use an environment variable to access them in /var/task/efs/