We would like to detect unusual config changes that can potentially cause production outage.
Such as, SecurityGroup new allow/deny rule, AuthZ policy change, Secret key/certificate rotation, IP subnet add/drop. The problem is the source of all of these activities is different, i.e., AWS IAM, Amazon EC2, internal prod services, envoy sidecar, etc.
Which of the technology would be best suitable to detect only IMP events (not all activity) from various sources all workload running on AWS and also Splunk Cloud?
Consider using a combination of Netflix Security Monkey and AWS Guard Duty.
You can achieve automated detection and alerting, as well as automated recovery based on policies with these tools.
For instance, you could detect SecurityGroup rule changes that allow unrestricted egress from EC2 instances and then revert those changes automatically.
It's unclear from your post whether you want to detect events within the Splunk Cloud infrastructure or if you want to detect events indicated in data going to Splunk using the Splunk capabilities. If the latter, then Splunk has extremely rich capabilities in their query language and integrated alerting functions. With Splunk you can also run arbitrary Python scripts in response to certain events, so what you can't analyze and alert on with native functionality or plugins, you could write code to achieve.
For continuous monitoring and detecting unusual configuration changes, I would suggest you look into AWS Config.
AWS Config enables you to assess, audit, and evaluate the configurations of your AWS resources. Config continuously monitors and records your AWS resource configurations and allows you to automate the evaluation of recorded configurations against desired configurations. Here is a list of supported AWS resources types and resource relationships with AWS Config https://docs.aws.amazon.com/config/latest/developerguide/resource-config-reference.html
Also as of Nov, 2019 - AWS Config launches support for third-party resources. You can now publish the configuration of third-party resources, such as GitHub repositories, Microsoft Active Directory resources, or any on-premises server into AWS Config using the new API. Here is more detail: https://docs.aws.amazon.com/config/latest/developerguide/customresources.html
If you have multiple AWS Account in your organization and want to detect changes there: https://docs.aws.amazon.com/config/latest/developerguide/aggregate-data.html
Lastly, if you already use Splunk Cloud in your enterprise and are looking for a consolidated view then, AWS Config is supported by Splunk Cloud as per their documentation too. https://aws.amazon.com/marketplace/pp/Splunk-Inc-Splunk-Cloud/B06XK299KV https://aws.amazon.com/marketplace/pp/Splunk-Inc-Splunk-Cloud/B06XK299KV
The key difference between Enterprise and Cloud is you have no control over the underlying infrastructure with Cloud. You can install and manage apps using the familiar GUI, but any changes to the platform (permissions changes, program installation, etc.) are done by Splunk support via a ticket. https://www.treeservicedenvercolorado.com/greeley-colorado.html
Image result for AWS Config. If you are using AWS Config rules, AWS Config continuously evaluates your AWS resource configurations for desired settings. <a href="https://www.rooferslakewood.com/">Lakewood Roofing Company</a>