Share storage bucket between apps - google-app-engine

Question

I have an internal tool that lets me edit configuration files and then the config files gets synced to Google Storage (* * * * * gsutil -m rsync -d /data/www/config_files/ gs://my-site.appspot.com/configs/).
How can I use these config files across multiple instances in Google App Engine? (I don't want to use the Google PHP SDK to read / write to the config files in the bucket).
Only thing I can come up with is making a cron.yaml file that downloads the configs from the bucket to /app/configs/ every minute, but then I'd have to reload php-fpm every minute as well.
app.yaml:
runtime: custom
env: flex
service: my-site
env_variables:
CONFIG_DIR: /app/configs
resources:
cpu: 1
memory_gb: 0.5
disk_size_gb: 10
automatic_scaling:
min_num_instances: 2
max_num_instances: 20
cpu_utilization:
target_utilization: 0.5
Dockerfile:
FROM eu.gcr.io/google-appengine/php71
RUN mkdir -p /app;
ADD . /app
RUN chmod -R a+r /app

Answer 1

I am assuming you are designing a solution where you can use pull requests on the GCS bucket to get configuration and update your apps en mass quickly.
There are many points in the process, depending on your exact flow, where you can insert a "please update now" command. For example, why can't you simply queue a task as you update the configuration in your GCS bucket? That task will basically down the configuration and redeloy your application.
Unless you are thinking about using multiple applications that have access to that bucket, and you want to be able to update them at the same time centrally. In that case, your cron job solution makes sense. Dan's suggestion definitely works, but I think you can make it easier by using version numbers. Simply have another file with a version number in it, the cron job pulls that file, compares it and then performs an update if the version is newer. It's very similar to Dan's solution except you don't really need to hash anything. If you are updating GCS with your configurations, might as well tag on another file with the version information.
Another solution is to expose a handler in all those applications, for example an "/update" handler. Whenever it's hit, the application performs the update. You can hit that handler whenever you actually update the configuration in your GCS. This is more of a push solution. The advantage is that you have more control over which applications gets the updates, this might be useful if you aren't sure about a certain configuration yet so you don't want to update everything at once.

Answer 2

We did not want to add a handler in our application for this. We thought it was best to use supervisord.
additional-supervisord.conf:
[program:sync-configs]
command = /app/scripts/sync_configs.sh
startsecs = 0
autorestart = false
startretries = 1
sync_configs.sh:
#!/usr/bin/env bash
while true; do
# Sync configs from Google Storage.
gsutil -m rsync -c -r ${CONFIG_BUCKET} /app/config
# Reload PHP-FPM
ps ax | grep php-fpm | cut -f2 -d" " - | xargs kill -s USR2
# Wait 60 seconds.
sleep 60
done
Dockerfile:
COPY additional-supervisord.conf /etc/supervisor/conf.d/