Access amplify env variables inside lambda function - amazon-web-services

Question

Is it possible to access the env variables inside lambda functions with amplify?
Here is an list with available env variables:
https://docs.aws.amazon.com/amplify/latest/userguide/environment-variables.html
From this list i need for example AWS_BRANCH. How do i access it inside the function?
I tried with process.env.AWS_BRANCH but its undefined.

Answer 1

There may be a better way than what I describe.
This comment uses jq to inject the build environment variable directly into your cloud formation.
jq '.Resources.LambdaFunction.Properties.Environment.Variables = .Resources.LambdaFunction.Properties.Environment.Variables + {"AWS_BRANCH": $AWS_BRANCH}' your-func-cloudformation-template.json > "$tmp" && mv "$tmp" your-func-cloudformation-template.json
You can put key-value pairs into the parameters.json file that sits next to the Lambda's xxxxxx-cloudformation-template.json file to inject the AWS_BRANCH value. e.g.
You'd need to inject that into the build script, perhaps via amplify.yml.
Second approach
You could modify the above to update an existing key in the parameters.json file. That will add it to your cloudformation and you can pull it into the resources environment vars. That seems a bit cleaner:
parameters.json
{
awsBranch: AWS_BRANCH
}
But then you still need to augment the build to inject the variable. The "best" way (until you find a better way) in my opinion would be to hard-code the value into each "environment" (e.g. dev, prod) in the amplify/team-provider-info.json file. Add it to the resources that need it and the value will be exposed to CloudFormation. Next, update the Lambda's CloudFormation and add it to the parameters and lambda environment vars.
Update your xxxxx-cloudformation-template.json file to have the property.
"Parameters": {
"awsBranch": {
"Type": "String",
"Description": "AWS_BRANCH from build environment vars"
},
Then in the lambda resource, convert the parameter to an environment var:
"Environment": {
"Variables": {
"AWS_BRANCH": {
"Ref": "awsBranch"
},
And then in your typescript code you can just access the parameter process.env.AWS_BRANCH.

Answer 2

I have found an workaround. I do it with the hooks: https://docs.amplify.aws/cli/project/command-hooks/
Here i use the pre-push.js hook that gets executed before the build.
Here is how i inject the environment variable AWS_BRANCH into my lambda:
First i need to read it:
let jsonFile = require("../backend/function/mylambda/mylambda-cloudformation-template.json")
Then i edit it:
jsonFile.Resources.LambdaFunction.Properties.Environment.Variables["AWS_BRANCH"] = process.env.AWS_BRANCH
Now i write the file back:
fs.writeFileSync("./amplify/backend/function/mylambda/mylambda-cloudformation-template.json", JSON.stringify(jsonFile))
This actually works. Now i can access process.env.AWS_BRANCH inside my lambda