Things to know
There are some things to know when you deploy Streamlit apps to App Engine.
The flexible environment is mandatory
You have to choose the flexible environment because it supports WebSockets and the standard environment does not.
Streamlit heavily relies on WebSockets for the communication between the server and the client.
This is a screenshot of https://cloud.google.com/appengine/docs/the-appengine-environments on 2021/12/12. The left is about the standard env and the right is the flexible env.
Custom runtime is not necessary
You do not have to use a custom runtime (a customized Docker image).
The flexible environment offers an official Python runtime as https://cloud.google.com/appengine/docs/flexible/python/runtime and you can use it.
You can also use a custom runtime. For example, it is a nice option when you want to use a different Python version from the one provided as the official runtime or when you already have a working Docker image.
NOTE:
As of 2021/12/12, the document says the Python version on the built-in Python3 runtime is 3.7.2
, but it is actually 3.6.10
known from sys.version
at least in the asia-northeast1
zone (Tokyo).
And Streamlit officially supports only Python>=3.7 while it is technically possible to be installed with Python 3.6, so maybe you should set up a custom runtime with Python>=3.7 following the section below.
The number of instances should be 1 if st.file_uploader
or st.download_button
is used
If your app contains st.file_uploader
or st.download_button
, you should set the maximum number of instances to 1. For that configuration, see https://cloud.google.com/appengine/docs/flexible/python/reference/app-yaml#services.
App Engine typically distributes the requests evenly among available instances so the file upload/download requests sometimes reach the instance different from the one where the session exists when there are multiple instances.
Errors as below appear in such cases.
When an error occurs with file upload: The file upload request reaches a server where the session does not exist and the server returns the 400 error code.
When an error occurs with file download: The file download request reaches a server where the session does not exist and the 404 response is returned.
This problem occurs with the file uploader/downloader components because they use normal stateless HTTP POST/GET requests while other components work on top of WebSocket connections consistent over sessions.
While I know this problem occurs at least with these components, I'm not sure whether there is another component which have this problem. I have not checked all.
NOTE:
Restricting the number of instances to 1 has a drawback as it may cause some downtimes.
As the document says, the flexible instances are restarted once a week, which leads to downtime when there are not multiple instances.
While this problem has already been stated in the following posts, the only solution suggested was to set the minimum number of instances as more than one, although it conflicts with the solution explained in this article. I could not find a solution that covers both problems.
- Do App Engine Flexible Environment VM instance restarts take advantage of automatic scaling? (Stack Overflow)
- Rolling restarts are causing are app engine app to go offline. Is there a way to change the config to prevent that from happening? (Stack Overflow)
NOTE:
App Engine offers the session affinity setting, but it does not help in this case because it is only for HTTP long polling like socket.io
as documented though this problem is due to a different reason.
Recipes
I will show some examples deploying Streamlit apps to App Engine in different situations.
Each of them can be deployed with the command below.
$ gcloud app deploy
All sample resources are available at https://github.com/whitphx/streamlit-appengine-samples .
Basic setup
This is the simplest one.
- No custom runtime
- No config on the number of instances (scaling)
- This app is not using file uploader or downloader.
https://github.com/whitphx/streamlit-appengine-samples/tree/main/helloworld
File list
.
├── app.yaml
├── requirements.txt
└── streamlit-app.py
app.yaml
runtime: python
env: flex
runtime_config:
python_version: 3
entrypoint: streamlit run streamlit-app.py --server.port $PORT
- The flexible environment is selected.
- The built-in Python3 runtime is used.
-
entrypoint
is configured to run the Streamlit process with the specified port number via the$PORT
environment variable.
requirements.txt
streamlit~=1.2.0
streamlit-app.py
import streamlit as st
st.title("App Engine sample app")
name = st.text_input("Your name?")
st.write(f"Hello, {name or 'world'}!")
File uploader and downloader
This is a sample with a file uploader and a downloader.
File list
.
├── app.yaml
├── requirements.txt
└── streamlit-app.py
app.yaml
runtime: python
env: flex
runtime_config:
python_version: 3
entrypoint: streamlit run streamlit-app.py --server.port $PORT
automatic_scaling:
max_num_instances: 1
# Or manual scaling as below:
# manual_scaling:
# instances: 1
In addition to the basic set-up, automatic_scaling.max_num_instances
is set to 1
.
If you want to use the manual scaling, use manual_scaling.instances
instead.
For these settings, see https://cloud.google.com/appengine/docs/flexible/python/reference/app-yaml#services.
requirements.txt
streamlit~=1.2.0
streamlit-app.py
import streamlit as st
st.title("App Engine sample app")
uploaded_file = st.file_uploader("Upload some file")
if uploaded_file:
st.write(f"{uploaded_file.name} was uploaded.")
st.download_button(f"Download {uploaded_file.name}", data=uploaded_file, file_name=uploaded_file.name)
Custom runtime
This sample uses a custom runtime with Dockerfile
.
Ref: https://cloud.google.com/appengine/docs/flexible/custom-runtimes/build
.
├── Dockerfile
├── app.yaml
├── requirements.txt
└── streamlit-app.py
app.yaml
runtime: custom
env: flex
- Set
runtime: custom
to use a custom runtime. -
entrypoint
is not needed as it is defined inDockerfile
.
Dockerfile
FROM gcr.io/google-appengine/python
# Ref:
# * https://github.com/GoogleCloudPlatform/python-runtime/blob/8cdc91a88cd67501ee5190c934c786a7e91e13f1/README.md#kubernetes-engine--other-docker-hosts
# * https://github.com/GoogleCloudPlatform/python-runtime/blob/8cdc91a88cd67501ee5190c934c786a7e91e13f1/scripts/testdata/hello_world_golden/Dockerfile
RUN virtualenv /env -p python3.7
ENV VIRTUAL_ENV /env
ENV PATH /env/bin:$PATH
ADD requirements.txt /app/
RUN pip install -r requirements.txt
ADD . /app
ENTRYPOINT [ "streamlit", "run", "streamlit-app.py", "--server.port", "8080" ]
- Use the base image officially provided by Google for App Engine,
gcr.io/google-appengine/python
.- App Engine has a health checking mechanism and the official base image is already configured for it.
- See https://cloud.google.com/appengine/docs/flexible/python/customizing-the-python-runtime
- Specify the Python version at virtualenv creation.
-
Some
Dockerfile
s of the test data in that repository can be references - The main process has to listen to the port 8080 in a custom runtime.
requirements.txt
streamlit~=1.2.0
streamlit-app.py
import sys
import streamlit as st
st.write(sys.version)
Top comments (2)
Thanks for the tutorial. This is Ibran, I have followed basic steps to deploy streamlit app to GCP App Engine and I have deployed successfully the streamlit app but when I browse the url I am getting service unavailable error. Please suggest how can I fix this issue.
Thanks for this helpful tutorial. I have a question about the basic example. When I add
streamlit-image-select
to theapp.yaml
file and then try to deploy I receive an error sayingCould not find a version that satisfies the requirement streamlit-image-select (from -r requirements.txt (line 2))
What do I need to do to install
streamlit-image-select
so that it will work on Google App Engine Flex?