Flask Load Balancing Using Nginx and Docker 

Thank you very much :D

Thank you :)

Thanks a lot :D

Most DB instances can take up a lot of load since they were designed that way. But when you seriously need to scale up DB instances, I recommend you take a look at horizontal DB scaling patterns. The most common ones are data replication (for read-heavy use cases) with a DB load balancer, or cluster-based sharding.

No question is noob level, and you are always welcome to ask! Docker itself is just a software that allows you to containerize and isolate applications. That itself isn't a Linux emulator, but it USES a Linux emulator/system to function. Docker is Linux based, that means that on any other OS that's not Linux (for example Windows), you need something to emulate a Linux system in order for Docker to run. So on Windows, you can try using WSL as it will emulate a Linux system. On Linux, you don't need to emulate anything as Docker will use the system's kernel and stuff to function.

Yes, run multiple unicorn instances on different ports, and then add each one's IP and port to upstream. For example, upstream gunicorn-servers { server 127.0.0.1:5000; server 127.0.0.1:5001; server 127.0.0.1:5002; } Now use that as your upstream for proxy-pass

In that case, I would use a service registry since the containers would have dynamic port allocation. Reverse proxy can look up the IPs and ports of the container instances through the service registry and forward the request to those

@@devguyahnaf thank you, I just thought to create a nginx load balancer on another server and upstream connection to the server instances domains. What about that?

@@Mar-kb8yq If you can hardcode the upstream connection with domains and they are connectable through VPC, then yeah go ahead. I was just talking about autoscaling and why I would use a service registry

@@devguyahnaf Ah ok, I like autoscaling, but for now I never did it, or course in future I want to learn it 😅. Thank you very much again. I will subscribe to your channel.

I have corrected a mistake in the flask part. Use `app.run(host="0.0.0.0", debug=True)`. The host="0.0.0.0" is important

@@devguyahnaf Thanks a lot for that correction, Ahnaf! It finally works!

same here, "unable to prepare context: path "context:app" not found.

Hi Phoenix, Seems I have figured out the issue, basically this means it cant find the Dockerfile....So I just replaced the word app with a period(.) . Essentially it just needs to be told where to find the Dockerfile, So with the (.) added, It looks in the CWD and then it runs successfully. So it should read context: .

what did you do? I did not get you :( @@kingleo188

It's the docker compose up command docker-compose up -d --scale service_name=5

Typo means typing mistake

@@devguyahnaf i got an issue regarding my nginx container wont build but the 3 app is builded any idea ?

i mean its created but keep exited

This deployment method isn't good for high scale production, something like a cloud container service with a managed load balancer or some kind of cluster L7 ingress would be better. This is just a way to quickly set up load balancing with docker compose for those who need it done fast and dirty. Primarily, the load balancing is round robin as far as I know. The upstream group has IP addresses which are provided by Docker compose during container build, as the containers' internal IPs are dynamic. And yes, there's some Docker magic going on here. It's also why I didn't go too deep into it, as a lot of stuff is managed by Docker's internal hostname providers and such. This isn't the optimised or recommended way of deploying it to prod, it's just a simple way for small setups with multiple containers. I don't really remember the specifics of this video at the moment, but do follow up with replies if you have any questions and my answer doesn't satisfy you.

@devguyahnaf maybe it's using dns based load balancing? I notice you just put "app" and it's able to load balance with just that, probably cos "app" returns a different ip each time?

@@rinket7779 You're probably right, I've just taken a look and Docker does some of that networking which includes hostname resolving, which implies that it's DNS based load balancing.