In the previous article, we're focusing on S3; now we'll focus on the Elastic Compute Cloud – commonly known as EC2.

1. EC2 Metadata Access

The AWS EC2MetadataUtils class provides static methods to access instance metadata like AMI Id and instance type. With Spring Cloud AWS we can inject this metadata directly using the @Value annotation.

This can be enabled by adding the @EnableContextInstanceData annotation over any of the configuration classes:

@Configuration
@EnableContextInstanceData
public class EC2EnableMetadata {
    //
}

In a Spring Boot environment, instance metadata is enabled by default which means this configuration is not required.

Then, we can inject the values:

@Value("${ami-id}")
private String amiId;

@Value("${hostname}")
private String hostname;

@Value("${instance-type}")
private String instanceType;

@Value("${services/domain}")
private String serviceDomain;

1.1. Custom Tags

Additionally, Spring also supports injection of user-defined tags. We can enable this by defining an attribute user-tags-map in context-instance-data using the following XML configuration:

<beans...>
    <aws-context:context-instance-data user-tags-map="instanceData"/>
</beans>

Now, let's inject the user-defined tags with the help of Spring expression syntax:

@Value("#{instanceData.myTagKey}")
private String myTagValue;

2. EC2 Client

Furthermore, if there are user tags configured for the instance, Spring will create an AmazonEC2 client which we can inject into our code using @Autowired:

@Autowired
private AmazonEC2 amazonEc2;

Please note that these features work only if the app is running on an EC2 instance.

3. Conclusion

This was a quick and to-the-point introduction to accessing EC2d data with Spring Cloud AWS.

In the next article of the series, we'll explore the RDS support.

As usual, the examples are available over on GitHub.

Next »
Spring Cloud AWS – RDS
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Spring Cloud AWS – S3
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