💻 What Is Sentinel? (And Why It’s Your Terraform Deployment’s Bodyguard)

Hey everyone 👋

If you’ve been diving into Terraform Cloud or Terraform Enterprise, you might have stumbled across something called Sentinel.

When I first heard the term, I thought it sounded like a superhero. And in a way… it is. It’s your infrastructure’s bodyguard — making sure only “safe” and “approved” changes ever get deployed.

Let me break it down the way I wish someone had explained it to me early on 👇

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🛡 Think of It Like a Security Guard at the Door
Imagine your Terraform deployments are like guests trying to get into an exclusive club (your production environment).

Normally, Terraform just checks their ID (syntax and provider checks) and lets them in.

But with Sentinel, you’ve got a professional bouncer who also checks:

• Are they wearing the right shoes (tags on EC2 instances)?
• Do they have the right membership (security group rules)?
• Are they on the approved guest list (compliant configurations)?

If they fail the test? They don’t get in — no matter how much they insist.

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⚙️ Why Use Sentinel?

✅ 1. Enforce Rules Before Deployment
Sentinel acts like a pre-deployment filter. You can define policies in code (like “block any EC2 without tags” or “disallow public 0.0.0.0/0 security group rules”) and Terraform will run these checks before an apply.

If a policy fails, you can:

• Block the change completely (Hard Mandatory)
• Warn but allow override (Soft Mandatory)
• Just log the violation (Advisory)

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🌍 2. Consistent Compliance Across Teams
With Sentinel, you’re not relying on everyone remembering “best practices.” Policies apply to every workspace they’re linked to, so no matter who runs the deployment — the same rules apply.

It’s like having a standardized checklist across every construction site.

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💥 3. Stop Mistakes Before They Hit Production
We’ve all been there — a security group accidentally left wide open to the world, or a missing tag that breaks cost allocation reports.

Sentinel stops these at the planning stage. No awkward “we need to roll this back” emails later.

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💬 How Sentinel Fits into Terraform Cloud

Sentinel works in a Policy Set → Workspace model:

1. Policies – Your rules, written in Sentinel’s policy language
2. Policy Sets – Groups of policies (e.g., “Security Rules”)
3. Workspaces – Where the policies are enforced on Terraform runs

When a workspace linked to a policy set runs a plan:

• Terraform Cloud executes the plan
• Sentinel checks the proposed changes against the policies
• Pass = Continue to apply
• Fail = Block or warn, depending on enforcement mode

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⚠️ A Few Things to Note

• Paid Feature: Sentinel is available in the Team & Governance tier and above (not in the free plan).
• It only checks Terraform-managed resources — manual AWS changes bypass it. For runtime enforcement, you’d pair Sentinel with something like AWS Config.
• Many orgs skip Sentinel entirely and still run large-scale Terraform deployments with free/open-source workflows — but if compliance and guardrails are top priority, it’s worth looking at.

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🧩 Final Thoughts
Sentinel isn’t about slowing you down — it’s about making sure you don’t deploy something you’ll regret later.

If you’re managing infrastructure at scale, or in industries where compliance matters, Sentinel turns your Terraform runs from “hope it works” into “know it’s safe.”

And yes… in my head, it still wears a cape 🦸‍♂️.

Are you using Sentinel in your Terraform workflows? Or are you managing compliance in other ways? I’d love to hear your take — drop me a comment or on LinkedIn! ☁️💬