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docs(lab1): add submission1 — deploy and failure exploration #1

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10 changes: 10 additions & 0 deletions app/gateway/main.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -336,6 +336,16 @@ async def _charge():
raise HTTPException(504, "Payment service timeout")
except httpx.HTTPStatusError as e:
raise HTTPException(e.response.status_code, "Payment failed")
except httpx.ConnectError:
log.warning(f"ConnectError caught for payments, returning graceful 503 for reservation {reservation_id}")
return JSONResponse(
status_code=503,
content={
"error": "payments_unavailable",
"message": "Payment service is temporarily down. Your reservation is held — try again in a few minutes.",
"reservation_id": reservation_id
}
)
except Exception as e:
log.error(f"payment error: {e}")
raise HTTPException(502, "Payment service unavailable")
Expand Down
200 changes: 200 additions & 0 deletions submissions/lab1.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,200 @@
# Task 1

#### 1
**docker compose ps**
`NAME IMAGE COMMAND SERVICE CREATED STATUS PORTS
`app-events-1 app-events "uvicorn main:app --…" events 2 minutes ago Up 2 minutes 0.0.0.0:8081->8081/tcp, [::]:8081->8081/tcp
`app-gateway-1 app-gateway "uvicorn main:app --…" gateway 2 minutes ago Up 2 minutes 0.0.0.0:3080->8080/tcp, [::]:3080->8080/tcp
`app-payments-1 app-payments "uvicorn main:app --…" payments 2 minutes ago Up 2 minutes 0.0.0.0:8082->8082/tcp, [::]:8082->8082/tcp
`app-postgres-1 postgres:17-alpine "docker-entrypoint.s…" postgres 2 minutes ago Up 2 minutes (healthy) 0.0.0.0:5432->5432/tcp, [::]:5432->5432/tcp
`app-redis-1 redis:7-alpine "docker-entrypoint.s…" redis 2 minutes ago Up 2 minutes (healthy) 0.0.0.0:6379->6379/tcp, [::]:6379->6379/tcp`

#### 2

**curl -s http://localhost:3080/events | python3 -m json.tool**
[
{
"id": 1,
"name": "Go Conference 2026",
"venue": "Main Hall A",
"date": "2026-09-15T09:00:00+00:00",
"total_tickets": 100,
"price_cents": 5000,
"available": 100
},
{
"id": 4,
"name": "Python Workshop",
"venue": "Lab 301",
"date": "2026-09-22T14:00:00+00:00",
"total_tickets": 25,
"price_cents": 2000,
"available": 25
},
{
"id": 2,
"name": "SRE Meetup",
"venue": "Room 204",
"date": "2026-10-01T18:00:00+00:00",
"total_tickets": 30,
"price_cents": 0,
"available": 30
},
{
"id": 5,
"name": "Kubernetes Deep Dive",
"venue": "Auditorium B",
"date": "2026-10-10T10:00:00+00:00",
"total_tickets": 80,
"price_cents": 8000,
"available": 80
},
{
"id": 3,
"name": "Cloud Native Summit",
"venue": "Expo Center",
"date": "2026-11-20T10:00:00+00:00",
"total_tickets": 500,
"price_cents": 15000,
"available": 500
}
]

**curl -s -X POST http://localhost:3080/events/1/reserve \
-H "Content-Type: application/json" \
-d '{"quantity": 1}' | python3 -m json.tool**
{
"reservation_id": "e00c0259-d45e-41c9-bd5d-4ec2bd6853e8",
"event_id": 1,
"quantity": 1,
"total_cents": 5000,
"expires_in_seconds": 300
}

**curl -s -X POST http://localhost:3080/reserve/e00c0259-d45e-41c9-bd5d-4ec2bd6853e8/pay | python3 -m json.tool**
{
"order_id": "e00c0259-d45e-41c9-bd5d-4ec2bd6853e8",
"event_id": 1,
"quantity": 1,
"total_cents": 5000,
"status": "confirmed"
}


#### 3
**curl -s http://localhost:3080/health | python3 -m json.tool**
{
"status": "healthy",
"checks": {
"events": "ok",
"payments": "ok",
"circuit_payments": "CLOSED"
}
}

#### 4
**Dependency map**
gateway → (EVENTS_URL) → events → (psycopg2) → postgres
gateway → (EVENTS_URL) → events → (redis-py) → redis
gateway → (PAYMENTS_URL) → payments


#### 5
| Component Killed | Events List | Reserve | Pay | Health Check | User Impact |
| ---------------- | ---------------------------------- | --------------------------------- | ---------------------------------- | -------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| payments | Works | Works | Fails(Payment service unavailable) | Degraded(payments: down) | Users can browse events and reserve tickets, but cannot complete any purchases. Critical path is broken at the final step. |
| events | Fails(Events service unavailable) | Fails(Events service unavailable) | Fails(Events service unavailable) | Degraded(events: down) | Total failure of the ticket catalog and reservation engine. If a payment is somehow forced, the order confirmation fails, leaving the system in an inconsistent state. |
| redis | Works | Fails(Gateway Timeout) | Fails(Cannot progress) | Degraded(redis: down) | Users can view the event catalog, but the entire reservation flow is completely blocked. |
| postgres | Fails (Events service unavailable) | Fails(Internal Server Error) | Fails (Cannot progress) | Degraded(events: degraded) | Completely paralyzes core business logic. Users can neither see the event catalog nor book tickets. |


#### 6

Target: http://localhost:3080 | RPS: 5 | Duration: 30s

10s requests=41 success=41 fail=0 error_rate=0%
10s requests=42 success=42 fail=0 error_rate=0%
10s requests=43 success=43 fail=0 error_rate=0%
10s requests=44 success=44 fail=0 error_rate=0%
20s requests=83 success=78 fail=5 error_rate=6.0%
20s requests=84 success=79 fail=5 error_rate=5.9%
20s requests=85 success=80 fail=5 error_rate=5.8%
20s requests=86 success=81 fail=5 error_rate=5.8%

Done. total=124 success=114 fail=10 error_rate=8.0%

# Task 2

**1. git diff app/gateway/main.py**
diff --git a/app/gateway/main.py b/app/gateway/main.py
index c86db33..c8559de 100644
--- a/app/gateway/main.py
+++ b/app/gateway/main.py
@@ -336,6 +336,16 @@ async def pay_reservation(reservation_id: str):
raise HTTPException(504, "Payment service timeout")
except httpx.HTTPStatusError as e:
raise HTTPException(e.response.status_code, "Payment failed")
+ except httpx.ConnectError:
+ log.warning(f"ConnectError caught for payments, returning graceful 503 for reservation {reservation_id}")
+ return JSONResponse(
+ status_code=503,
+ content={
+ "error": "payments_unavailable",
+ "message": "Payment service is temporarily down. Your reservation is held — try again in a few minutes.",
+ "reservation_id": reservation_id
+ }
+ )
except Exception as e:
log.error(f"payment error: {e}")
raise HTTPException(502, "Payment service unavailable")


**2.**

**curl -s -X POST http://localhost:3080/events/1/reserve \
-H "Content-Type: application/json" -d '{"quantity": 1}'**
{"reservation_id":"af91ade2-05f8-481c-863d-b2a1741b11c1","event_id":1,"quantity":1,"total_cents":5000,"expires_in_seconds":300}

**curl -s -X POST http://localhost:3080/reserve/af91ade2-05f8-481c-863d-b2a1741b11c1/pa**
{"error":"payments_unavailable","message":"Payment service is temporarily down. Your reservation is held — try again in a few minutes.","reservation_id":"af91ade2-05f8-481c-863d-b2a1741b11c1"}

# Task 3

**Why starring repositories matters in open source:**
Stars help bookmark interesting projects for later reference while indicating their popularity and community trust. Additionally, they appear on your profile to show your interests and encourage maintainers by increasing project visibility.

**How following developers helps in team projects and professional growth:**
Following others helps you see what developers are working on and discover new projects through their activity. It allows you to stay updated on classmates' work for future collaboration and build professional connections beyond the classroom.

# Bonus Task

### Stats tables:
1. **B1**
NAME CPU % MEM USAGE / LIMIT NET I/O PIDS
app-gateway-1 0.21% 38.11MiB / 7.754GiB 11.9kB / 7.63kB 2
app-payments-1 0.20% 39.06MiB / 7.754GiB 2.8kB / 126B 1
app-events-1 0.29% 41MiB / 7.754GiB 14.3kB / 11.1kB 2
app-postgres-1 0.01% 23.57MiB / 7.754GiB 108kB / 115kB 8
app-redis-1 0.84% 9.336MiB / 7.754GiB 38.9kB / 13.6kB 6
2. **B2**
NAME CPU % MEM USAGE / LIMIT NET I/O PIDS
app-gateway-1 6.62% 38.79MiB / 7.754GiB 529kB / 507kB 2
app-payments-1 0.32% 39.86MiB / 7.754GiB 18.6kB / 11.1kB 2
app-events-1 3.22% 41.7MiB / 7.754GiB 463kB / 620kB 2
app-postgres-1 0.96% 24.25MiB / 7.754GiB 364kB / 406kB 8
app-redis-1 5.42% 9.355MiB / 7.754GiB 103kB / 40.7kB 6
3. **B3**
NAME CPU % MEM USAGE / LIMIT NET I/O PIDS
app-payments-1 0.22% 33.73MiB / 7.754GiB 10.2kB / 5.68kB 2
app-gateway-1 4.57% 39.16MiB / 7.754GiB 949kB / 914kB 2
app-events-1 2.39% 41.77MiB / 7.754GiB 821kB / 1.1MB 2
app-postgres-1 0.54% 24.32MiB / 7.754GiB 564kB / 645kB 8
app-redis-1 0.55% 3.496MiB / 7.754GiB 140kB / 56kB 6

**Which service uses the most memory? Does it change under load?**
The `events` service uses the most memory (~41 MiB). Its consumption remains highly stable and barely changes under load (varying by less than 1 MiB).
**Which service uses the most CPU under load? Why?**
The `gateway` service uses the most CPU (6.62%) because it is the central entry point. It has to process all incoming traffic, manage routing, and handle JSON serialization for every request.
**How does fault injection in payments affect resource usage in gateway?**
Introducing latency in `payments` decreases the `gateway` CPU usage (from 6.62% to 4.57%). This happens because the gateway becomes I/O-bound, spending more time holding connections open and waiting for responses rather than executing active CPU computations.