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main.py	main.py
metrics.py	metrics.py
requirements.txt	requirements.txt

Day-01: DevOps FastAPI App Project.

A FastAPI application exposing operational endpoints for health checks, metrics, and failure simulation, providing a practical foundation for learning observability, reliability, and deployment automation.

Overview

This app provides:

Health check: /health → returns {"status":"ok"} or {"status":"fail"} depending on /fail or /recover calls. Used by readiness probe.
Demo endpoint: /hello → basic endpoint for generating traffic. Can also be used for liveness probe.
Prometheus metrics: /metrics → exposes metrics for monitoring requests and latency.
Metrics snapshot: /metrics-snapshot → developer-friendly snapshot of current request counts (local testing only).
Fail endpoint: /fail (POST) → sets /health to fail (HTTP 500), simulating a pod NotReady state.
Recover endpoint: /recover (POST) → restores /health to OK (HTTP 200), marking pod Ready.
Crash endpoint: /crash (POST) → kills the application process immediately, triggering the liveness probe to restart the container.

All metrics are collected via middleware to track request counts and latency.

Endpoints

Endpoint	Method	Description
`/health`	GET	Returns health status. Can return `{"status":"ok"}` or `{"status":"fail"}` depending on `/fail` or `/recover` calls. Used by readiness probe.
`/hello`	GET	Sample endpoint for generating traffic. Used by liveness probe.
`/metrics`	GET	Prometheus metrics endpoint for monitoring request counts and latency.
`/metrics-snapshot`	GET	Developer-friendly snapshot of current request counts (local testing only).
`/fail`	POST	Sets the `/health` endpoint to return HTTP 500 → simulates pod not ready.
`/recover`	POST	Restores `/health` endpoint to return HTTP 200 → pod marked Ready again.
`/crash`	POST	Immediately kills the application process → triggers liveness probe to restart the container.

The last three end-points /fail,/recover and /crash ar used extensively in Day-03 to test out the liveness probe and the readiness probe.

============================================================================================================================================

How to Run This App Locally:-

Clone the repository first:

root@ubuntu-host ~ ➜  git clone https://github.com/Janemils/Devops-Project-1.git
Cloning into 'Devops-Project-1'...
Username for 'https://github.com': <enter-your-username>
Password for 'https://Janemils@github.com': <enter-your-PAT>
remote: Enumerating objects: 294, done.
remote: Counting objects: 100% (123/123), done.
remote: Compressing objects: 100% (77/77), done.
remote: Total 294 (delta 54), reused 79 (delta 28), pack-reused 171 (from 1)
Receiving objects: 100% (294/294), 18.30 MiB | 31.02 MiB/s, done.
Resolving deltas: 100% (95/95), done.

root@ubuntu-host ~ ➜  cd Devops-Project-1/Day-01

root@ubuntu-host Devops-Project-1/Day-01 on  main via 🐍 ➜

Install dependencies:

# Currently, I am in a virtual environment:
root@ubuntu-host Devops-Project-1/Day-01 on  main via 🐍 v3.12.3 (venv) ➜  pip install -r requirements.txt
Collecting annotated-doc==0.0.4 (from -r requirements.txt (line 1))
  Downloading annotated_doc-0.0.4-py3-none-any.whl.metadata (6.6 kB)
Collecting annotated-types==0.7.0 (from -r requirements.txt (line 2))
  Downloading annotated_types-0.7.0-py3-none-any.whl.metadata (15 kB)
...................

# If successful, you should see these three packages:
root@ubuntu-host Devops-Project-1/Day-01 on  main via 🐍 v3.12.3 (venv) ➜  pip list
Package           Version
----------------- -------
fastapi           0.128.0
prometheus_client 0.24.1
uvicorn           0.40.0

Troubleshooting Tip:
If you face this issue while running the above command:

Tip

Issue: `pip: command not found`

Error

-bash: pip: command not found

Cause Some minimal Ubuntu installations do not include pip or the packages required to create Python virtual environments by default.

Resolution Install pip and the required Python packages:

sudo add-apt-repository universe
sudo apt update
sudo apt install python3-pip
sudo apt install python3-full -y

Create and activate a virtual environment:

python3 -m venv venv
source venv/bin/activate

Then install the project dependencies:

pip install -r requirements.txt

Why use a virtual environment?
A virtual environment isolates project dependencies from the system Python installation, preventing version conflicts and ensuring a reproducible development setup.

============================================================================================================================================

Run the app:

root@ubuntu-host Devops-Project-1/Day-01 on  main via 🐍 v3.12.3 (venv) ➜  uvicorn main:app --reload --host 0.0.0.0 --port 8000
INFO:     Will watch for changes in these directories: ['/root/Devops-Project-1/Day-01']
INFO:     Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [5761] using StatReload
INFO:     Started server process [5769]
INFO:     Waiting for application startup.
INFO:     Application startup complete.

============================================================================================================================================

Test endpoints:

Now open a new terminal and let's test out all the endpoints:

Health check

root@ubuntu-host ~ ➜  curl http://localhost:8000/health
{"status":"ok"}

Basic hello endpoint

root@ubuntu-host ~ ➜  curl http://localhost:8000/hello
{"message":"Hello from DevOps app"}

Prometheus metrics

root@ubuntu-host ~ ➜  curl http://localhost:8000/metrics
# HELP python_gc_objects_collected_total Objects collected during gc
# TYPE python_gc_objects_collected_total counter
python_gc_objects_collected_total{generation="0"} 410.0
python_gc_objects_collected_total{generation="1"} 71.0
python_gc_objects_collected_total{generation="2"} 0.0
# HELP python_gc_objects_uncollectable_total Uncollectable objects found during GC
# TYPE python_gc_objects_uncollectable_total counter
python_gc_objects_uncollectable_total{generation="0"} 0.0
python_gc_objects_uncollectable_total{generation="1"} 0.0
python_gc_objects_uncollectable_total{generation="2"} 0.0
# HELP python_gc_collections_total Number of times this generation was collected
# TYPE python_gc_collections_total counter
python_gc_collections_total{generation="0"} 105.0
python_gc_collections_total{generation="1"} 9.0
python_gc_collections_total{generation="2"} 0.0
# HELP python_info Python platform information
# TYPE python_info gauge
python_info{implementation="CPython",major="3",minor="12",patchlevel="3",version="3.12.3"} 1.0
# HELP process_virtual_memory_bytes Virtual memory size in bytes.
# TYPE process_virtual_memory_bytes gauge
process_virtual_memory_bytes 1.34344704e+08
# HELP process_resident_memory_bytes Resident memory size in bytes.
# TYPE process_resident_memory_bytes gauge
process_resident_memory_bytes 4.5871104e+07
# HELP process_start_time_seconds Start time of the process since unix epoch in seconds.
# TYPE process_start_time_seconds gauge
process_start_time_seconds 1.78108209202e+09
# HELP process_cpu_seconds_total Total user and system CPU time spent in seconds.
# TYPE process_cpu_seconds_total counter
process_cpu_seconds_total 0.27
# HELP process_open_fds Number of open file descriptors.
# TYPE process_open_fds gauge
process_open_fds 13.0
# HELP process_max_fds Maximum number of open file descriptors.
# TYPE process_max_fds gauge
process_max_fds 1024.0
# HELP http_requests_total Total HTTP requests
# TYPE http_requests_total counter
http_requests_total{endpoint="/health",method="GET",status="200"} 1.0
http_requests_total{endpoint="/hello",method="GET",status="200"} 1.0
# HELP http_requests_created Total HTTP requests
# TYPE http_requests_created gauge
http_requests_created{endpoint="/health",method="GET",status="200"} 1.781082116288453e+09
http_requests_created{endpoint="/hello",method="GET",status="200"} 1.7810821407909093e+09
# HELP http_request_latency_seconds Request latency in seconds
# TYPE http_request_latency_seconds histogram
http_request_latency_seconds_bucket{le="0.005"} 2.0
http_request_latency_seconds_bucket{le="0.01"} 2.0
http_request_latency_seconds_bucket{le="0.025"} 2.0
http_request_latency_seconds_bucket{le="0.05"} 2.0
http_request_latency_seconds_bucket{le="0.075"} 2.0
http_request_latency_seconds_bucket{le="0.1"} 2.0
http_request_latency_seconds_bucket{le="0.25"} 2.0
http_request_latency_seconds_bucket{le="0.5"} 2.0
http_request_latency_seconds_bucket{le="0.75"} 2.0
http_request_latency_seconds_bucket{le="1.0"} 2.0
http_request_latency_seconds_bucket{le="2.5"} 2.0
http_request_latency_seconds_bucket{le="5.0"} 2.0
http_request_latency_seconds_bucket{le="7.5"} 2.0
http_request_latency_seconds_bucket{le="10.0"} 2.0
http_request_latency_seconds_bucket{le="+Inf"} 2.0
http_request_latency_seconds_count 2.0
http_request_latency_seconds_sum 0.0013682842254638672
# HELP http_request_latency_seconds_created Request latency in seconds
# TYPE http_request_latency_seconds_created gauge
http_request_latency_seconds_created 1.7810820925906413e+09

To fail the health check:

root@ubuntu-host ~ ➜  curl -X POST http://localhost:8000/fail
{"message":"health check failing"}

# Let's cross-verify if it actually failed:
root@ubuntu-host ~ ➜  curl http://localhost:8000/health
{"status":"fail"}

# We can also check from the application logs:
INFO:     127.0.0.1:43148 - "POST /fail HTTP/1.1" 200 OK
INFO:     127.0.0.1:59990 - "GET /health HTTP/1.1" 500 Internal Server Error

To recover the failed health check:

root@ubuntu-host ~ ➜  curl -X POST http://localhost:8000/recover
{"message":"health restored"}

# Let's cross-verify if it actually restored:
root@ubuntu-host ~ ➜  curl http://localhost:8000/health
{"status":"ok"}

# Application Logs:
INFO:     127.0.0.1:51266 - "POST /recover HTTP/1.1" 200 OK
INFO:     127.0.0.1:51280 - "GET /health HTTP/1.1" 200 OK

To manipulate an internal server error:

root@ubuntu-host ~ ➜  curl  http://localhost:8000/error
{"details":"Internal Server Error"}

# Application Logs:
INFO:     127.0.0.1:59888 - "GET /error HTTP/1.1" 500 Internal Server Error

To crash the application (i.e; just kill the process)

root@ubuntu-host ~ ➜  curl -X POST http://localhost:8000/crash
curl: (52) Empty reply from server

# Let's cross-verify if the application actually crashed:
root@ubuntu-host ~ ✖ curl http://localhost:8000/health

# This will hang as the application has crashed. This is expected. You can re-run the uvicorn command to get the application running again.

Debugging: current counts.

This endpoint is purely for debugging purpose only. Use it to validate if the http_request counts are being incremented successfully.

curl http://localhost:8000/metrics-snapshot

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README.md

Day-01: DevOps FastAPI App Project.

Overview

Endpoints

How to Run This App Locally:-

Clone the repository first:

Install dependencies:

Issue: `pip: command not found`

Run the app:

Test endpoints:

Health check

Basic hello endpoint

Prometheus metrics

To fail the health check:

To recover the failed health check:

To manipulate an internal server error:

To crash the application (i.e; just kill the process)

Debugging: current counts.

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parent directory

README.md

Day-01: DevOps FastAPI App Project.

Overview

Endpoints

How to Run This App Locally:-

Clone the repository first:

Install dependencies:

Issue: pip: command not found

Run the app:

Test endpoints:

Health check

Basic hello endpoint

Prometheus metrics

To fail the health check:

To recover the failed health check:

To manipulate an internal server error:

To crash the application (i.e; just kill the process)

Debugging: current counts.

Issue: `pip: command not found`