Outcome
By the end of this lesson, you will be able to preview a change before it runs, read a blast radius honestly, and decide when an assistant should stop and ask you.
| Tier | Engineer |
| JTBD | ”Not break production while moving fast.” |
| Personas | Platform Engineer · SRE · Developer |
| Prerequisites | M6.6.L3 |
| Time | 9 minutes |
| Bloom verb | Preview (Apply), Read (Understand), Decide (Evaluate) |
1. Concept
Two habits separate a useful assistant from a dangerous one, and neither is about the assistant.
PREVIEW ask what a change would do before it does itBLAST RADIUS ask what else is attached to the thing you are touchingBoth exist as first-class reads, which means “check first” costs one question rather than a policy document.
What a blast radius can and cannot see
IT SEES the dependents the platform knows about: what runs on this, what fronts it, what stores its data
IT CANNOT SEE a hardcoded IP in somebody's script, a cron on a laptop, a partner pulling from your endpointAn edge it cannot see is still an edge. The honest use of blast radius is to shrink the unknown, not to eliminate it.
When an assistant should stop
STOP AND ASK IF the action is tier 3 the resource is in production the blast radius names something you did not expect you are acting during an incident and you are not the commanderThe first is enforced by the server. The other three are yours.
2. Demo
YOU "Stop the db-staging instance."
ASSISTANT blast radius: 3 dependents api-staging service, will lose its database worker-staging service, will lose its database nightly-etl job, runs at 02:00
eligibility: allowed, tier 2
"This has three dependents. Do you want me to stop it anyway?"
YOU "No. Stop the two services first, then the database."The value was not in the refusal. It was in the list.
3. Hands-on (6 min)
1. Pick a resource with something attached to it.2. Ask for its blast radius before doing anything.3. Ask for a preview of the change you were going to make, and read what it says it would do.4. Now make the change, and compare the result with the preview.5. Write down one dependency the platform could not have known about.Do it through MCP. The same task you just did in the console, asked in one sentence.
BEFORE A non-production resource with at least one dependent: a database behind a service, or a load balancer in front of one.ASK "What is the blast radius of stopping this, and what would the remediation actually change?"CHECK the dependents it lists against what you know. The gap between those two lists is the part of your estate the platform cannot see, and it is worth knowing before an incident rather than during one.Tools behind it: get_blast_radius (read, Explore), check_eligibility (read, Introspect), preview_remediation (read, Optimize). The full catalogue is at zop.dev/learn/mcp-tools.
4. Knowledge check
Q1
Blast radius reports no dependents. The correct reading:
A. Nothing depends on this resource
B. The resource is safe to delete
C. Nothing the platform knows about depends on it
D. Discovery has not run
Show answer
Correct: C. The report covers edges the platform can see. A hardcoded address in somebody’s script is a real dependency and an invisible one, which is why an empty result lowers risk rather than removing it.
Q2
Why is preview a read rather than a write?
A. Because it changes nothing: it reports what a change would do
B. Because it is cheaper
C. Because it needs no permission
D. Because it runs in a sandbox
Show answer
Correct: A. A preview that changed anything would not be a preview. It is available at every level for exactly that reason, so “check first” is never gated behind write access.
Q3
During an incident, which of these should an assistant do without stopping to ask?
A. Deregister the cluster
B. Read the alert, the state history, and the blast radius
C. Stop every resource in the account
D. Roll back every service
Show answer
Correct: B. Reads are free and they are what the first ten minutes are made of. A and C are exactly the actions that need a human sentence behind them, and D treats a symptom you have not diagnosed yet.
5. Apply
Make previewing a habit rather than a rule. The habit survives a bad night; the rule gets skipped on one.
KEEP one blast radius that surprised you one dependency it could not seeRelated lessons
- L5: Diagnosing a bad deploy
- T2.M2.15.L1: What blast radius answers
- T5.M5.7.L2: The cost incident commander