Check env variables in serverless.yml file (Serverless Framework) - node.js

Question

I am new to using serverless framework and I would like to check that env variables inside serverless.yml are changing according to the stage I am on. Here is what I have in serverless.yml:
service: items
custom:
customDomain:
domainName: api.app.com
certificateName: '*.api.app.com'
basePath: ''
stage: ${self:provider.stage} <=== (Variable to check)
createRoute53Record: true
webpack:
webpackConfig: ./webpack.config.js
includeModules: true
serverless-iam-roles-per-function:
defaultInherit: true
.......
provider:
name: aws
runtime: nodejs8.10
......
......
process_updates:
handler: handler.processUpdates
iamRoleStatements:
- Effect: "Allow"
Action:
- s3:*
Resource:
- "arn:aws:s3:::${file(./config.${self:provider.stage}.json):items_updates}/*"
Config.dev.json:
{
"items_updates": "dev-items-updates"
}
Config.prod.json:
{
"items_updates": "prod-items-updates"
}
So, I would like to know if there is a way to print the following variables
${self:provider.stage} and ${file(./config.${self:provider.stage}.json):items_updates} when the deployment is happening. And is there best practice using different env with serverless framework?
Thanks in advance !

Answer 1

Plugin?
If you want to tie into Serverless lifecycle events, and do stuff, one typical approach would be to write a plugin.
I found the learning curve with Serverless plugin development to be quite gentle, and would recommend writing one to any Serverless user that hasn't done so.
However, sometimes a plugin is overkill, or undesirable for other reasons.
Workaround
One very handy (yet often overlooked) feature of Serverless is that it can resolve variables from javascript files.
Note the exported function with this signature:
module.exports = (serverless) => { ... }
This serverless object gives you access to all sorts of stuff:
Command line args can be found on serverless.processedInput.options.
Your service can be found at serverless.service.
Concrete Case
In your case, you could either put your ${env}-items-updates data directly into a .js function, or have your function read up the file(s).
For the sake of simplicity, I'll assume you're willing to stuff the data right into the function. I'll also illustrate using only a singe items-updates.js file, rather than separate files per stage.
items-updates.js:
module.exports = (serverless) => {
const stage = serverless.service.provider.stage;
serverless.cli.log(`Resolving items-updates for stage ${stage}`);
switch (stage) {
case 'dev':
return {}; // Your dev-items-updates here
case 'prod':
return {}; // Your prod-items-updates here
}
}
Then in your iamRoleStatements:
Resource:
- ${file(./items-updates.js)}
Note: While the example above shows a default export, I do typically use named exports, so I can put more than one resource in a single js file.