Technical Articles
Create simple Flask REST API using Cloud Foundry
Hi All,
I am writing this blog to describe some easy steps to deploy a Python Flask based REST API application on the SAP cloud foundry environment.
Python is very useful to deal with many requirements, since it has so many powerful libraries. In my case, I recently used it to connect web application and TensorFlow serving for object detection. The python application resizes image file and converts data format.
For Flask logging, please see another article “Logging from Python Flask application deployed on Cloud Foundry”.
Environment
Local PC
- Windows 10 Professional
- Python 3.6.6 on Anaconda
- Flask 1.0.2
- cf CLI 6.37.0
Cloud Foundry
- Python Build pack 1.6.20
- CF Trial (Europe – Frankfurt)
Prerequisites
- your space is created on Cloud Foundry environment
- cf CLI is installed on Local PC(see the official page for the installation)
Procedure
1. Prepare for python application
The python application is on my Github repository, so just clone the repository is also OK here.
1.1. Application directory
Create an application directory on local PC. I created the one named “cloudfoundry-python-flask-sample”.
1.2. Flask application(hello.py)
The application is quite simple, because it just return “Hello World”. It works also on local window PC.
from flask import Flask
import os
app = Flask(__name__)
# Port number is required to fetch from env variable
# http://docs.cloudfoundry.org/devguide/deploy-apps/environment-variable.html#PORT
cf_port = os.getenv("PORT")
# Only get method by default
@app.route('/')
def hello():
return 'Hello World'
if __name__ == '__main__':
if cf_port is None:
app.run(host='0.0.0.0', port=5000, debug=True)
else:
app.run(host='0.0.0.0', port=int(cf_port), debug=True)
1.3. Add Flask library to file “requirements.txt”
Add Flask library to file “requirements.txt”. If you want other libraries, just add them.
Flask
1.4. Python runtime version(runtime.txt)
Just write python runtime version. The version should be listed here. As of 2018/12/12 I used python Buildpack 1.6.20, which was default on SAP Cloud Platform CF.
python-3.6.6
To check cf buildpack version, just use “cf buildpacks” command.
1.5. Manifest(manifest.yml)
This is so simple application that it does not need much resources. Please make sure don’t allocate much resources.
---
applications:
- memory: 128MB
disk_quota: 256MB
random-route: true
1.6. Commands run the application(Procfile)
Here just write down a command, which runs hello.py application.
web: python hello.py
2. Deploy the application to cloud foundry
2.1. Check cloud foundry API endpoint
See the API endpoint from SAP Cloud Platform Cockpit.
2.2. Login Cloud Foundry using cf CLI
Run command prompt and login to the cloud foundry.
cf api https://api.cf.eu10.hana.ondemand.com
cf login
2.3. Deploy the application
Change current directory and deploy the application.
cf push <application name>
3. Check the result
3.1. Check the result
See the application status via SAP Cloud Platform Cockpit. There is an application Routes, so just click the link.
Here I can see “Hello World”!
Conclusion
The advantage to use Cloud Foundry is that we can concentrate on development. For me it is so helpful that there is few time to setup environment like OS, python.
Hi Yohei Fukuhara
THX, for you blog. It was a great help understanding Python deployment to Cloud Foundry.
I noticed that the app is accessible from the Internet without further login.
Is that correct or did I miss some step? Can you explain how to implement check for authenticated user / authorization role, please?
Cheers,
Alej
Hi,
Yes, you are right.
I haven't implemented any authentication checks.
I haven't check how to implement it.
Regards,
Yohei
Awesome tutorial for those who are learning how to develop/deploy python app to CF
I am trying to follow this and get almost all the way but during push I get this error:
Cell 578cfd64-547a-47eb-82d0-710b4a3fbd7a creating container for instance 6b6707da-7d3c-4305-81e5-f96bc447f13a
Cell 578cfd64-547a-47eb-82d0-710b4a3fbd7a successfully created container for instance 6b6707da-7d3c-4305-81e5-f96bc447f13a
Downloading app package...
Error staging application: App staging failed in the buildpack compile phase
FAILED
Any idea what is happening?
Will you share the whole log?
I kept at it and I had to change the Python version to 3.8.1 and it worked. At some point I saw a message indicating what versions were supported but not sure where I saw that.
I also added in the manifest.yaml something about the buildpack and cflinux -- I don't have it right now -- but I don't think that did anything.
Thanks for very helpful blog
Hi Yohei,
Awesome Tutorial.
Any idea how to debug the cloud api.
Regards
Alok
> Any idea how to debug the cloud api.
I have no idea.
I usually output logs and see how processes work.
I seldom develop apps, so I'm not sure if some good way exists.
Yohei
Hi Yohei,
Awesome Tutorial!
After this step:
How can we run the app to start without a HTTP request ? Thank you very much~
Best,
Wenxi
Hi,
It stars automatically with my example.
If you want to start tasks from cli, use the below command, though I don't remember if there are prerequisites.
cf run-task <cf app name> --command "python <file name>.py" --name taskfromcli
Regards,
Yohei
Hi Yohei,
Indeed a nice blog. I am also using Python for one of the project where flask and chromadb is used.
In BAS I was trying to install chromadb but it was not getting install as it required Visual C++ build tools, so I did development in VScode and trying to push the app in CF.
But getting this error -- " 2023-08-11T15:07:59.61+0530 [APP/PROC/WEB/0] ERR Traceback (most recent call last):
2023-08-11T15:07:59.61+0530 [APP/PROC/WEB/0] ERR File "/home/vcap/app/app.py", line 5, in <module>
2023-08-11T15:07:59.61+0530 [APP/PROC/WEB/0] ERR from flask import Flask, render_template, request, jsonify
2023-08-11T15:07:59.61+0530 [APP/PROC/WEB/0] ERR ModuleNotFoundError: No module named 'flask'"
Not sure if you can suggest which can fix the error, it will be appreciated.
Regards,
Abhijeet
Hi,
I suspect if you failed to install Flask package.
Please check the below chapter.
1.3. Add Flask library to file “requirements.txt”
You can check if Flask is successfully installed using ssh.
Regards,
Yohei
Thanks Yohei for your comment.
I have added flask==2.0.1 in requirements.txt file. only only this module but other modules are also there.
Regards,
Abhijeet
Hi,
Though I haven't check it, please try "Flask".
I think python packages are case dependant.
Regards,
Yohei
Hi Abhijeet
I'm also getting same error. Did you find any solution for this issue??
Hi Mayank,
Instead of BAS I used VS code and deploy from there. it was there in BAS while testing locally as there are multiple dependencies missing in BAS.
Regards,
Abhijeet