Architecture Flask vs FastAPI

This seemed a little interesting, so i ran a little tests with ApacheBench:

Flask

from flask import Flask
from flask_restful import Resource, Api


app = Flask(__name__)
api = Api(app)


class Root(Resource):
    def get(self):
        return {"message": "hello"}


api.add_resource(Root, "/")

FastAPI

from fastapi import FastAPI


app = FastAPI(debug=False)


@app.get("/")
async def root():
    return {"message": "hello"}

I ran 2 tests for FastAPI, there was a huge difference:

  1. gunicorn -w 4 -k uvicorn.workers.UvicornWorker fast_api:app
  2. uvicorn fast_api:app --reload

So here is the benchmarking results for 5000 requests with a concurrency of 500:

FastAPI with Uvicorn Workers

Concurrency Level:      500
Time taken for tests:   0.577 seconds
Complete requests:      5000
Failed requests:        0
Total transferred:      720000 bytes
HTML transferred:       95000 bytes
Requests per second:    8665.48 [#/sec] (mean)
Time per request:       57.700 [ms] (mean)
Time per request:       0.115 [ms] (mean, across all concurrent requests)
Transfer rate:          1218.58 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    6   4.5      6      30
Processing:     6   49  21.7     45     126
Waiting:        1   42  19.0     39     124
Total:         12   56  21.8     53     127

Percentage of the requests served within a certain time (ms)
  50%     53
  66%     64
  75%     69
  80%     73
  90%     81
  95%     98
  98%    112
  99%    116
 100%    127 (longest request)

FastAPI – Pure Uvicorn

Concurrency Level:      500
Time taken for tests:   1.562 seconds
Complete requests:      5000
Failed requests:        0
Total transferred:      720000 bytes
HTML transferred:       95000 bytes
Requests per second:    3200.62 [#/sec] (mean)
Time per request:       156.220 [ms] (mean)
Time per request:       0.312 [ms] (mean, across all concurrent requests)
Transfer rate:          450.09 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    8   4.8      7      24
Processing:    26  144  13.1    143     195
Waiting:        2  132  13.1    130     181
Total:         26  152  12.6    150     203

Percentage of the requests served within a certain time (ms)
  50%    150
  66%    155
  75%    158
  80%    160
  90%    166
  95%    171
  98%    195
  99%    199
 100%    203 (longest request)

For Flask:

Concurrency Level:      500
Time taken for tests:   27.827 seconds
Complete requests:      5000
Failed requests:        0
Total transferred:      830000 bytes
HTML transferred:       105000 bytes
Requests per second:    179.68 [#/sec] (mean)
Time per request:       2782.653 [ms] (mean)
Time per request:       5.565 [ms] (mean, across all concurrent requests)
Transfer rate:          29.13 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0   87 293.2      0    3047
Processing:    14 1140 4131.5    136   26794
Waiting:        1 1140 4131.5    135   26794
Total:         14 1227 4359.9    136   27819

Percentage of the requests served within a certain time (ms)
  50%    136
  66%    148
  75%    179
  80%    198
  90%    295
  95%   7839
  98%  14518
  99%  27765
 100%  27819 (longest request)

Total results

Flask: Time taken for tests: 27.827 seconds

FastAPI – Uvicorn: Time taken for tests: 1.562 seconds

FastAPI – Uvicorn Workers: Time taken for tests: 0.577 seconds


With Uvicorn Workers FastAPI is nearly 48x faster than Flask, which is very understandable. ASGI vs WSGI, so i ran with 1 concurreny:

FastAPI – UvicornWorkers: Time taken for tests: 1.615 seconds

FastAPI – Pure Uvicorn: Time taken for tests: 2.681 seconds

Flask: Time taken for tests: 5.541 seconds

I ran more tests to test out Flask with a production server.

5000 Request 1000 Concurrency

Flask with Waitress

Server Software:        waitress
Server Hostname:        127.0.0.1
Server Port:            8000

Document Path:          /
Document Length:        21 bytes

Concurrency Level:      1000
Time taken for tests:   3.403 seconds
Complete requests:      5000
Failed requests:        0
Total transferred:      830000 bytes
HTML transferred:       105000 bytes
Requests per second:    1469.47 [#/sec] (mean)
Time per request:       680.516 [ms] (mean)
Time per request:       0.681 [ms] (mean, across all concurrent requests)
Transfer rate:          238.22 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    4   8.6      0      30
Processing:    31  607 156.3    659     754
Waiting:        1  607 156.3    658     753
Total:         31  611 148.4    660     754

Percentage of the requests served within a certain time (ms)
  50%    660
  66%    678
  75%    685
  80%    691
  90%    702
  95%    728
  98%    743
  99%    750
 100%    754 (longest request)

Gunicorn with Uvicorn Workers

Server Software:        uvicorn
Server Hostname:        127.0.0.1
Server Port:            8000

Document Path:          /
Document Length:        19 bytes

Concurrency Level:      1000
Time taken for tests:   0.634 seconds
Complete requests:      5000
Failed requests:        0
Total transferred:      720000 bytes
HTML transferred:       95000 bytes
Requests per second:    7891.28 [#/sec] (mean)
Time per request:       126.722 [ms] (mean)
Time per request:       0.127 [ms] (mean, across all concurrent requests)
Transfer rate:          1109.71 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0   28  13.8     30      62
Processing:    18   89  35.6     86     203
Waiting:        1   75  33.3     70     171
Total:         20  118  34.4    116     243

Percentage of the requests served within a certain time (ms)
  50%    116
  66%    126
  75%    133
  80%    137
  90%    161
  95%    189
  98%    217
  99%    230
 100%    243 (longest request)

Pure Uvicorn, but this time 4 workers uvicorn fastapi:app --workers 4

Server Software:        uvicorn
Server Hostname:        127.0.0.1
Server Port:            8000

Document Path:          /
Document Length:        19 bytes

Concurrency Level:      1000
Time taken for tests:   1.147 seconds
Complete requests:      5000
Failed requests:        0
Total transferred:      720000 bytes
HTML transferred:       95000 bytes
Requests per second:    4359.68 [#/sec] (mean)
Time per request:       229.375 [ms] (mean)
Time per request:       0.229 [ms] (mean, across all concurrent requests)
Transfer rate:          613.08 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0   20  16.3     17      70
Processing:    17  190  96.8    171     501
Waiting:        3  173  93.0    151     448
Total:         51  210  96.4    184     533

Percentage of the requests served within a certain time (ms)
  50%    184
  66%    209
  75%    241
  80%    260
  90%    324
  95%    476
  98%    504
  99%    514
 100%    533 (longest request)

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