(Since the origin of this POC, Spring Cloud AWS has developed its bootstrapping to remove the need for this.)
So, basically, when you create a Spring Cloud AWS application, and set up your unit
tests, you'll need to turn off Spring Cloud AWS, and create a custom @TestConfiguration
for your test AWS clients. That's because Spring Cloud AWS hooks into the Spring ApplicationContext
initialization cycle, (which hooks into the JUnit 5 execution cycle) and runs its own network
requests before any of your application is initialized.
Or...
You can use the same code for testing and production, but hack into the JUnit 5 initialization cycle and set up some mock AWS instance configuration endpoints as well as LocalStack, before Spring Cloud AWS starts making network requests.
Then you hack into the AWS Java SDK initialization cycle, and point the AWS regions which you're using, towards your LocalStack instance, after disabling TLS certificate verification for the AWS Java SDK.
How?
You can hook into the JUnit 5 extension initialization cycle before Spring Cloud AWS, if you
introduce a static field to your unit test, annotated with o.j.j.a.e.RegisterExtension.
The lifecycle events you want to hook into are BeforeAllCallback and AfterAllCallback.
You can create a better LocalStackContainer, which exposes LocalStack through a fixed port,
which you can then configure into src/test/resources/com/amazonaws/regions/override/regions.xml
which is a magic file path which will be loaded by
c.a.r.LegacyRegionXmlMetadataBuilder.loadOverrideMetadataIfExists
if it exists in the classpath.
Finally, Spring Cloud AWS uses the AWS Java SDK to read the instance configuration, in case
the application is running on a EC2 instance, and you've given that instance a role and attached
policies to that role, which allow that instance access to things such as S3 buckets.
Normally, this AWS API endpoint would generate some temporary keys according to those
policies, and serve them through a magic API endpoint. We'll want to hook into this
process in our JUnit 5 extension initialization, by setting the system property
com.amazonaws.sdk.ec2MetadataServiceEndpointOverride to our own mock endpoint URL.
Set a field modification watchpoint on com.amazonaws.AmazonWebServiceClient.endpoint.
Add a file called src/test/resources/com/amazonaws/regions/override/regions.xml.
It will be loaded in com.amazonaws.regions.LegacyRegionXmlMetadataBuilder.loadOverrideMetadataIfExists.
Just add some nonsense to the file, and a stack trace will present itself.
The parser for regions.xml is com.amazonaws.regions.RegionMetadataParser.internalParse.
spring-attic/spring-cloud-aws#570
https://cloud.spring.io/spring-cloud-static/spring-cloud-aws/2.2.2.RELEASE/reference/html/