Serverless stage environment variables using dotenv (.env) - aws-lambda

Question

I'm new to serverless,
So far I was be able to deploy and use .env for the app.
then, under provider in stage property in serverless.yml file, I change it to different stage. I also made new.env.{stage}.
after re-deploy using sls deploy, It still reads the default .env file.
the documentation states:
The framework looks for .env and .env.{stage} files in service directory and then tries to load them using dotenv. If .env.{stage} is found, .env will not be loaded. If stage is not explicitly defined, it defaults to dev.
So, I still don't understand "If stage is not explicitly defined, it defaults to dev". How to explicitly define it?

Answer 1

The dotenv File is choosen based on your stage property configuration. You need to explicitly define the stage property in your serverless.yaml or set it within your deployment command.
This will use the .env.dev file
useDotenv: true
provider:
name: aws
stage: dev # dev [default], stage, prod
memorySize: 3008
timeout: 30
Or you set the stage property via deploy command.
This will use the .env.prod file
sls deploy --stage prod

Answer 2

In your serverless.yml you need to define the stage property inside the provider object.
Example:
provider:
name: aws
[...]
stage: prod

Answer 3

As Feb 2023 I'm going to attempt to give my solution. I'm using the Nx tootling for monorepo (this shouldn't matter but just in case) and I'm using the serverless.ts instead.
I see the purpose of this to be to enhance the developer experience in the sense that it is nice to just nx run users:serve --stage=test (in my case using Nx) or sls offline --stage=test and serverless to be able to load the appropriate variables for that specific environment.
Some people went the route of using several .env.<stage> per environment. I tried to go this route but because I'm not that good of a developer I couldn't make it work. The approach that worked for the was to concatenate variable names inside the serverless.ts. Let me explain...
I'm using just one .env file instead but changing variable names based on the --stage. The magic is happening in the serverless.ts
// .env
STAGE_development=test
DB_NAME_development=mycraftypal
DB_USER_development=postgres
DB_PASSWORD_development=abcde1234
DB_PORT_development=5432
READER_development=localhost // this could be aws rds uri per db instances
WRITER_development=localhost // this could be aws rds uri per db instances
# TEST
STAGE_test=test
DB_NAME_test=mycraftypal
DB_USER_test=postgres
DB_PASSWORD_test=abcde1234
DB_PORT_test=5433
READER_test=localhost // this could be aws rds uri per db instances
WRITER_test=localhost // this could be aws rds uri per db instances
// serverless.base.ts or serverless.ts based on your configuration
...
useDotenv: true, // this property is at the root level
...
provider: {
...
stage: '${opt:stage, "development"}', // get the --stage flag value or default to development
...,
environment: {
STAGE: '${env:STAGE_${self:provider.stage}}}',
DB_NAME: '${env:DB_NAME_${self:provider.stage}}',
DB_USER: '${env:DB_USER_${self:provider.stage}}',
DB_PASSWORD: '${env:DB_PASSWORD_${self:provider.stage}}',
READER: '${env:READER_${self:provider.stage}}',
WRITER: '${env:WRITER_${self:provider.stage}}',
DB_PORT: '${env:DB_PORT_${self:provider.stage}}',
AWS_NODEJS_CONNECTION_REUSE_ENABLED: '1',
}
...
}
When one is utilizing the useDotenv: true, serverless loads your variables from the .env and puts them in the env variable so you can access them env:STAGE.
Now I can access the variable with dynamic stage like so ${env:DB_PORT_${self:provider.stage}}. If you look at the .env file each variable has the ..._<stage> at the end. In this way I can retrieve dynamically each value.
I'm still figuring it out since I don't want to have the word production in my url but still get the values dynamically and since I'm concatenating this value ${env:DB_PORT_${self:provider.stage}}... then the actual variable becomes DB_PORT_ instead of DB_PORT.