Chapter 3: Record traffic

Your agent records everything the app receives and sends while the traffic driver runs. Every later chapter replays this recording.

Time: 1 to 2 minutes.

Prompt

Go

Use the record-traffic skill to record the tutorial app in mock-lab/tutorial/go while its traffic driver runs, including its Postgres and CNCF API calls. Name the recording baseline.

Java

Use the record-traffic skill to record the tutorial app in mock-lab/tutorial/java while its traffic driver runs, including its Postgres and CNCF API calls. Name the recording baseline.

Python

Use the record-traffic skill to record the tutorial app in mock-lab/tutorial/python while its traffic driver runs, including its Postgres and CNCF API calls. Name the recording baseline.

Node.js

Use the record-traffic skill to record the tutorial app in mock-lab/tutorial/node while its traffic driver runs, including its Postgres and CNCF API calls. Name the recording baseline.

What the agent does

The record-traffic skill:

• Starts the app under proxymock record with --map 15432=postgres://localhost:5432 and DATABASE_URL pointed at port 15432, so proxymock sits between the app and Postgres. Outbound HTTPS to the CNCF API goes through proxymock's proxy on port 4140.
• Waits for /healthz on port 4143, proxymock's inbound port, which forwards to the app on 8080.
• Runs the traffic driver against http://localhost:4143 so proxymock sees every inbound request.
• Names the recording proxymock/recorded-baseline, following the skill's recorded-<name> convention.
• Counts what was captured per host and endpoint, then summarizes it with proxymock report (the proxymock-summarize-recording skill).
• Stops proxymock and the app and leaves Postgres running.

What you should see

The capture, by directory, and the skill's ### Result block. Trimmed:

| Directory                    | What it holds                  | Pairs |
|------------------------------|--------------------------------|-------|
| localhost/                   | Inbound requests to the app    | 136   |
| demo-api.trafficreplay.com/  | CNCF API calls over HTTPS      | 70    |
| localhost-5432/              | Postgres messages              | 1,075 |

### Result
- **Ran:** `proxymock record --out proxymock/recorded-baseline --map 15432=postgres://localhost:5432 --app-port 8080 --app-health-endpoint /healthz -- go run .` in mock-lab/tutorial/go, traffic from `go run ./cmd/traffic http://localhost:4143`
- **Outcome:** complete
- **Numbers:** 136 inbound pairs across 6/6 endpoints; outbound hosts 1/1 (demo-api.trafficreplay.com, 70 pairs); databases 1/1 (Postgres, 1,075 pairs); 8 error-status pairs (6 inbound 4xx + 2 upstream 404, all expected)
- **Artifacts:** mock-lab/tutorial/go/proxymock/recorded-baseline/ (5.5 MB, includes proxymock.log)
- **Next:** proxymock-regression-test — "make a regression gate for the tutorial app from the baseline recording"

The inbound count is 136 because the skill's own readiness check is recorded with the driver's 135 requests. The error statuses are the driver's bad requests and two unknown projects, so they are expected. The proxymock report summary scores the recording for performance, reliability and security. Its security findings are the Server header from the CNCF API and the email addresses in the demo orders.

The counts differ a little by language. The Java recording, for example, holds 1,095 Postgres pairs instead of 1,075, because the JDBC driver sends its own session setup.

Follow the Result's Next line later. Chapters 4 and 5 tune the mocks and tests first, so the regression test in chapter 6 is trustworthy.

If it goes wrong

• The agent says record-traffic is not a loaded skill. Your skills are an older copy. Install them again as in Start here, then restart the agent.
• Java: every catalog call returns 502 catalog unavailable and the app log shows PKIX path validation failed. The Java truststore proxymock injects is older than its certificate. Rebuild it with proxymock admin certs --jks, with JAVA_HOME set to your JDK, then delete the partial recording and record again.
• The database is on another port. If you set TUTORIAL_DB_PORT in chapter 2, map to that port: --map 15432=postgres://localhost:<port>.

See PostgreSQL for how --map records a database, and Java with proxymock for JVM proxy and truststore settings.

Manual equivalent

Run proxymock with the app in one terminal and the traffic driver in another. Stop proxymock with ctrl-c when the driver finishes.

Go

cd mock-lab/tutorial/go
DATABASE_URL='postgres://tutorial:tutorial@localhost:15432/tutorial?sslmode=disable' \
  proxymock record --out proxymock/recorded-baseline \
  --map 15432=postgres://localhost:5432 \
  --app-port 8080 --app-health-endpoint /healthz -- go run .
# second terminal
go run ./cmd/traffic http://localhost:4143

Java

cd mock-lab/tutorial/java
DATABASE_URL='postgres://tutorial:tutorial@localhost:15432/tutorial?sslmode=disable' \
  proxymock record --out proxymock/recorded-baseline \
  --map 15432=postgres://localhost:5432 \
  --app-port 8080 --app-health-endpoint /healthz -- java -jar target/tutorial-orders.jar
# second terminal
./mvnw -q compile exec:java -Dexec.args="http://localhost:4143"

Python

cd mock-lab/tutorial/python
source .venv/bin/activate
DATABASE_URL='postgres://tutorial:tutorial@localhost:15432/tutorial?sslmode=disable' \
  proxymock record --out proxymock/recorded-baseline \
  --map 15432=postgres://localhost:5432 \
  --app-port 8080 --app-health-endpoint /healthz -- python app.py
# second terminal
python traffic.py http://localhost:4143

Node.js

cd mock-lab/tutorial/node
DATABASE_URL='postgres://tutorial:tutorial@localhost:15432/tutorial?sslmode=disable' \
  proxymock record --out proxymock/recorded-baseline \
  --map 15432=postgres://localhost:5432 \
  --app-port 8080 --app-health-endpoint /healthz -- node server.js
# second terminal
node traffic.mjs http://localhost:4143

Then summarize the recording:

proxymock report --in proxymock/recorded-baseline --format prompt

Next

Chapter 4: Tune the mocks