Synopsis:
I couldn’t find an easy guide to follow other
than the google app engines lengthy tutorial, so in hope of saving others a bit of time I made this nifty post 😉. I go over
deploying a flask application in google app engines ‘standard’ environment and some potential pitfalls you might encounter on the way.
Standard Environment:
Currently the google app engine's provided local dev server (dev_appserver.py)
only supports the standard environment so I decided to release on the standard environment
for this reason. I felt that it’d be faster to reach a working deployment if I
could fail very quickly locally, however the flex environment is superior in various ways.
Step 1: Create an App ID
You'll first need to create an application on google cloud services which you can get to by going to the main console.
Step 2: Enabling Services
You may need to enable various services before deploying. If you navigate to the consoles of the various services it should ask if you want the service enabled for your application
I enabled:
Step 3: Setting up your local environment
For this next sections you probably want to make sure your using a virtual environment and produce the correct requirements.txt file. The final results will yield the relatively few files you need to add to work with google app engine. You'll also need to be sure you have the SDK for App Engine
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| Required Files For App Engine |
Creating app.yaml
The app.yaml file describes properties on how to handle routing and the deployment your application.
The runtime argument is always python27 for standard environment.
The handlers are used for routing to different components (e.g. static content).
Specifically for my site everything is routed to my main.py:
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| main.app -> main.py, app variable |
If your using cloud storage in your app you can specify the "CLOUD_STORAGE_BUCKET" environment variable and that's what libraries the ndb will use as the default bucket.
**NOTE**
When I was making my app.yaml assumed the allowed properties were the same regardless of which environment your deploying into.
This caused the extremely nondescript error:
Updating service [default]...failed. ERROR: (gcloud.app.deploy) INVALID_ARGUMENT: The request is invalid.
Many wasted hours because the key "env" is required when deploying on flexible environment, but not allowed when deploying on 😕😕standard😕😕
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| app.yaml for flexible enviroment |
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| app.yaml for standard enviroment |
Adding Libraries And Dependencies:
Unlike the flex environment the standard environment won't use your requirements.txt
Instead you must bundle the required libraries in a folder. When you create the appengine_config.py file in your root folder you can configure additional locations for where to find requisite libraries.
I used "pip install -t lib -r requirements.txt" to save all the required libraries to a deployable folder
Further instructions can be found here
Technically you can add specific libraries in your app.yaml but I was already so skeptical that I figured I avoid the frustration by just loading all my required files with the mechanism I knew to work.
Step 4: Local Testing
Setting up gcloud:
If this is the first app your setting up you should run:
gcloud init
You'll get a prompted to set default regions, email address, and project id.
You should also set the default project with:
gcloud config set project <Your Project ID>
You should also login with:
gcloud auth application-default login
I had some weird threading bug on my client and the recommended fix was running:
gcloud config set app/num_file_upload_processes 1
Once that's set up you can run your app locally using dev_appserver.py
dev_appserver.py --port <port num> <path\to\your\app.yaml>
** Note **
I had trouble with all flask versions greater than 0.10.2 as the dependent library "click" fails to work with the local server, so I decided I could live with a lower version of Flask.....
Step 5: Deploying
Once you've fixed all the kinks in your local environment you can deploy by using
gcloud app deploy app.yamlI had problems with some of my files not getting deployed so you may need to change the standard skipped files.
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| What it should look like if things work..... |
**NOTE**
If you end up with an "INVALID_ARGUMENT: The request is invalid." error validate your app.yaml as there is little to no validation of this file when testing using the local server.
Going Past Deployment:
Originally google actually offered a service to deploy directly from your repository but they deprecated this feature. I find this particularly sad because that's one of my favorite features offered by competitors like elastic bean stalk. It's especially aggregating as it wasn't always clear on app engine what files were going actually to get deployed, as by default app engine skips various files (e.g. those beginning with "." or ending with ".pyc")
An alternative is to use Travis CI's to trigger an app cloud update after a success build.
