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Custom provider resources
Sometimes you want to add custom provider resources to your service to use provider specific functionality which is not yet available through events or plugins. Serverless has you covered and enables you a convenient way to add those resources with the help of the resources section in the serverless.yml file.
Note: Your custom resources are merged on top of the resources Serverless defines. This gives you the power to overwrite existing resources easily, even the ones that are created automatically by Serverless. You need to be careful though to not disrupt Serverless functionality.
Adding custom provider resources
Serverless uses the services resources object as a place to add more custom resources.
You can use this place to add custom provider resources by writing the resource definition in the provider specific YAML syntax inside the resources object. You can also use Serverless Variables for sensitive data or reusable configuration in your resources templates.
Note: You'll have the whole flexibility to overwrite / attach any kind of resource to your CloudFormation stack. You can add Resources, Outputs or even overwrite the Description. Please be cautious as overwriting existing parts of your CloudFormation stack might introduce unexpected behavior.
# serverless.yml
resources:
Resources:
CustomProviderResource:
Type: ResourceType
Properties:
Key: Value
Outputs:
CustomOutput:
Description: "Description for my output"
Value: "My Custom Output"
Example custom resources - S3 bucket
Sometimes you need an extra S3 bucket to store some data in (say, thumbnails). This works by adding an extra S3 Bucket Resource to your serverless.yml:
service: lambda-screenshots
provider: aws
functions:
...
resources:
Resources:
ThumbnailsBucket:
Type: AWS::S3::Bucket
Properties:
# You can also set properties for the resource, based on the CloudFormation properties
BucketName: my-awesome-thumbnails
# Or you could reference an environment variable
# BucketName: ${env:BUCKET_NAME}
Now that you have this additional resource defined in your serverless.yml file, you can simply run serverless deploy and that will deploy these custom resources for you along with your service and set up the additional bucket for you.
Conclusion
The resources section inside the serverless.yml file is a place
where you can add custom, provider specific resource definitions which should be created on service deployment.
It gives you access to the whole feature set your provider offers and makes Serverless even more extensible.
The last thing we need to learn is how we can remove our service. Let's take a look at this now.