What is the best way to train a team on a new CI/CD system while keeping the old one running?

Alright, listen up, because I’ve seen more teams hemorrhage cash on dual CI/CD runtimes than on forgotten EC2 instances in us-east-1. You’re trying to train a team on a new system while the old one is still operational? That's like trying to teach someone to rebuild an engine while the car is still doing 80 on the highway. The meter is running on both systems, and your team's cognitive load is about to spike your cloud bill.

The core strategy is to treat this like a phased cloud migration. You don't lift-and-shift; you **parallel run with a clear cost and complexity kill switch**. Here's the painful, detailed breakdown:

**Phase 1: The "Shadow Pipeline" Gambit**
* Pick **one non-critical, low-frequency pipeline** to be your sacrificial lamb. A weekly report generation, a documentation build, something that won't trigger a P1 incident.
* Rebuild it **exactly** in the new system (GitHub Actions, GitLab CI, whatever). The goal isn't optimization yet; it's familiarity. This is where you document the translation pain.
* **Crucially, run them in parallel but only the old one deploys.** The new one runs in "dry-run" or only builds artifacts. You're now paying for double compute. Track that cost. I use a script to tag these training runs for later analysis.

```bash
# Example: Tagging training runs in AWS for cost allocation
aws resourcegroupstaggingapi tag-resources
--resource-arn-list arn:aws:codebuild:us-east-1:123456789012:build/project:training-run-*
--tags Key=Environment,Value=Training Key=CI-CD-Migration-Phase,Value=1
```

**Phase 2: The Rotating "Pipeline Pilot" Program**
* Mandate that every new feature branch **must** have its pipeline built in the new system. The old system remains the source of truth for merging to main. This forces hands-on learning.
* Assign a rotating "pilot" from the team each week. Their job is to be the expert, unblock others, and **document the gotchas**. This prevents creating a single point of failure (and knowledge).
* **Secrets migration is your silent killer.** Use this phase to test your secrets injection strategy. If you're moving from, say, Jenkins to CircleCI, don't just copy-paste. Use the pilot phase to validate the new vault integration. A single leaked secret in a log could cost you more than the training.

**Phase 3: The Cut-Over (Where Bills Go to Die or Thrive)**
* By now, you should have a library of translated pipeline snippets and known cost traps (e.g., the new system spins up larger default workers, or has longer minimum billing durations).
* Switch the **entire pipeline for a single, medium-stakes application**. Not your monolith. Do it on a Tuesday morning, not a Friday afternoon. Keep the old pipeline configuration archived but disabled. The "kill switch" is re-enabling it.
* **Measure everything:** build time, cost per build, failure rate. Compare it directly to the old system's metrics. This is the FinOps part. If the new system is 20% faster but 300% more expensive per build, you've just trained your team on a financial regression.

The biggest mistake? Letting the old and new systems run indefinitely "for safety." Set a hard date to sunset the old pipelines, starting with the non-critical ones. Every day of overlap is double billing on compute, storage for artifacts, and network egress. Your cloud bill is too high.