How do you generate realistic cloud activity for security testing?

Scripts and APIs are probably the best way to keep activity running once the environment is understood. I would combine routine actions such as logins, deployments, storage access, and identity changes with a controlled set of security scenarios. Run them on a schedule and verify that the SIEM sees the expected events and that the rules do not generate excessive noise. A dedicated environment is important so the tests cannot affect production.

A good repeatable approach is to build a disposable test subscription with Terraform. Use scheduled scripts, CI jobs, and controlled scenarios to generate both normal user activity and known security events. Treat every scenario like a test case with an expected detection, then regularly destroy and recreate the environment. That way you're testing the monitoring controls and making sure the infrastructure code still produces the intended baseline.

I would start manually rather than automating everything immediately. Set up a dedicated test tenant, study real incident reports, reproduce the attack chain step by step, and deliberately configure the relevant services and permissions. Once you understand what each action should look like in the logs, test detection and remediation, then repeat the scenario to confirm it is blocked or alerted on. After that, automate the environment and activity with PowerShell, Terraform, or APIs. The manual phase takes longer, but it prevents you from automating a flawed understanding of the attack.

For failure-oriented testing, a chaos or cloud-simulation tool can be useful, especially for checking how monitoring responds when services or configurations break. I would use that alongside an infrastructure-as-code baseline and scripted activity rather than relying on it alone. The hardest part is usually maintaining believable background activity; scheduled workflows, automated test accounts, and periodic rebuilds help prevent the lab from becoming an untouched snapshot.