Build the safeguards
Eight explained steps, a source example and a checkpoint at each decision.
Read the tutorialDelivery / Database migrations / Infrastructure as code
Run it. Change it. Verify it.
Start in your browser, then take the complete Safe Rollout Lab into an independent local environment.
Try it without installing a toolchain
- Open the playground and keep its default scenario.
- Run the comparison and read the results before opening the code.
- Change the scenario, run again, and identify which decision changed.
- Open View the code, choose a source file and read the explanation above it.
- Reset the environment, including a run that is still pending.
Run your downloaded copy
Download and extract the ZIP into a new folder. With Python 3 installed, open a terminal in that folder and run the command below. It serves only this package on loopback; opening index.html directly is insufficient for workers and WebAssembly.
python preview.pyOpen http://127.0.0.1:4210/ in your browser. Stop the server with Ctrl+C. The prebuilt preview needs no dependency installation and makes no automatic requests to another site. The source code and notices are included alongside it.
Run the native exercise
The commands below start in the extracted package root. Node-based examples require Node 24 or later; the Go adapter requires Go 1.27 or later; the Python adapter requires Python 3.11 or later. Install only the toolchain used by this lab. Exact dependency versions and the Node lockfile are in the download.
npm ci
npm test
node src/rollout/local-release.mjsAll safeguarded data reads return 200 across mixed versions and application rollback. The destructive path produces missing-column errors. The contract gate refuses to remove a column while an old reader remains.
Read GETTING_STARTED.md for the native request examples and shutdown steps. Native servers bind to 127.0.0.1. The optional monitoring containers expose only loopback ports. They are a separate exercise from the browser preview.
Make one meaningful change
Add an old writer that changes full_name after the backfill. Demonstrate the divergence, then implement a compatibility writer or another explicit synchronization policy. Do not retire the old field until old writes are gone.
Add the expected result first, reproduce the failure, repair it, then rerun the native and browser checks. Use npm run rebuild for the Node/browser examples. The Go package includes rebuild_wasm.py; the Python package includes refresh_source.py.
Record what you learned
Capture the scenario, edition, input records, observed outcome and the test that checks it. Explain one alternative you rejected and why. Avoid converting a small local result into a throughput, security or accuracy claim about a production system.
Read the primary documentation
Verantos emphasizes incremental infrastructure changes, trusted CI/CD and explicit validation and rollback plans.
Choose your next step
Compare the alternatives
Understand where each pattern helps and which tradeoffs remain.
Compare approachesRun and extend it locally
Download the independent environment, run the native checks and try a specific extension.
Open the how-to guideLab discussion / Safe Rollout Lab
What would you try next?
Ask about the code, compare an approach, or describe an edge case. Reader comments are reviewed before publication.
Code walkthrough
Follow the implementation in code.
These short excerpts connect the lab’s behavior to its implementation. Each example links to the full tutorial step for its context, tradeoffs and checkpoint. Names and dependencies belong to that source; the excerpts are not standalone programs.
Expand without removing the old contract
Add the new field while keeping the old one. This gives new code somewhere to read without breaking existing consumers. The right production DDL strategy also depends on locking, table size, defaults and the database version; this tiny table demonstrates compatibility only.
ALTER TABLE profiles ADD COLUMN display_name text;Backfill and keep writes compatible
Copy existing values, then maintain both representations during the transition. A one-time backfill is insufficient if an old writer continues changing only the old field. This exercise’s compatible writer sets both fields; the extension challenge deliberately introduces an old writer.
UPDATE profiles SET display_name=full_name;
UPDATE profiles SET full_name=$1,display_name=$1 WHERE id=$2;Gate traffic on meaningful readiness
The readiness preset marks the canary unready. The browser models the traffic decision, while its data reads remain real. A production readiness probe must reflect the dependencies required to serve safely; a process merely listening on a port may not be sufficient.
if (!canaryReady) keepTrafficOnVersionOne();