How to Fix 502 Bad Gateway Errors in Production Flask Apps Running NGINX & Gunicorn

Today I deployed some new code to production for a Flask app that I’m currently building. On my local machine the code which I wrote was running fine without any issues. However, after deploying the code to production I noticed my new endpoint was not working at all and was consistently returning 502 Bad Gateway errors.

A few things I tried tweaking to fix this included updating the config files for NGINX and Gunicorn and explicitly setting timeout durations because the new code that I pushed to production was pretty long running and slow, so I thought maybe something was just timing out. However, after updating my timeout settings in my NGINX and Gunicorn config files to 5 minutes, my code continued to fail in production.

Then I happened to stumble upon a forum post where someone mentioned that this error can sometimes occur if you run out of memory or compute resources. My production server at the time was pretty weak, especially compared to my laptop, running a single CPU with 1 gigabyte of RAM.

The next fix I tried was bumping the resources for my server via DigitalOcean’s server hosting dashboard. And voila! After bumping the resources to 2 CPUs and 4 gigabytes of RAM my code started running as expected, and the 502 bad gateway error went away.

So there you have it. If you have tried bumping the timeout setting for NGINX and Gunicorn and are still running into 502 bad gateway errors, try allocating more CPU and memory resources to your production flask app, and that may fix the issue, especially if the code that is failing is something long running and slow.

UPDATE: I ended up having to bump the resources again, this time to 4 CPUs with 8 gigabytes of RAM.


How to Detect Collisions Between Humanoids in Roblox

Really quick blog post here tonight on how to detect collisions between Humanoids in Roblox. My script is named DetectCollisionsBetweenHumanoids and I’ve placed this script under ServerScriptService. Please note, that I have some code in my example which displays text on the users screen whenever a collision is detected, you can ignore this part of the code which displays that a collision has occurred on the screen:

-- DisplayTextModule is some code I use to display text on screen for testing, if you see this in a code snippet, ignore this part
local DisplayTextModule = require(script.Parent.Parent.StarterGui.ScreenGui.Frame.TextLabel.DisplayTextModuleScript)
local Players = game:GetService("Players")
-- Works for R15, not sure if this works for R6 or not
local function partIsHumanoid(part)
if part.Name == "Head" then
return true
elseif part.Name == "UpperTorso" then
return true
elseif part.Name == "LowerTorso" then
return true
elseif part.Name == "LeftFoot" then
return true
elseif part.Name == "LeftLowerLeg" then
return true
elseif part.Name == "LeftUpperLeg" then
return true
elseif part.Name == "RightFoot" then
return true
elseif part.Name == "RightLowerLeg" then
return true
elseif part.Name == "RightUpperLeg" then
return true
elseif part.Name == "LeftHand" then
return true
elseif part.Name == "LeftLowerArm" then
return true
elseif part.Name == "LeftUpperArm" then
return true
elseif part.Name == "RightHand" then
return true
elseif part.Name == "RightLowerArm" then
return true
elseif part.Name == "RightUpperArm" then
return true
return false
local function onPlayerAdded(player)
local character = player.Character or player.CharacterAdded:Wait()
local humanoid = character:WaitForChild("Humanoid")
local timestampStr = tostring(os.time("!*t")))
if partIsHumanoid(otherPart) then
DisplayTextModule.Display("Collision w/ R15: " .. otherPart.Name)

How to Display Text on Screen Programmatically in Roblox

I’m currently working on building my first game in Roblox, and I need to be able to print out some information to the screen for debugging. Normally you can just use “print()” to display text for debugging / texting purposes, but I’ve noticed that this doesn’t work when you’re testing multiplayer functionality. Right now I’m trying to detect collisions between Humanoids, and print just isn’t working for me in this specific circumstance since I have to run the game in multiplayer mode (print works fine for me when just running the game as a single player however).

Okay so let’s get to it, how to display text on screen programmatically in Roblox. First you’ll need to add ScreenGui to the StarterGui in Roblox Studio. If you need help with this, reference this tutorial from Roblox on how to add a scoreboard:

Then you’ll want to add a TextLabel to your ScreenGui, and after that, add a ModuleScript called DisplayTextModuleScript.

Then under ServerScriptServer, add another script called PrintToOnScreenLogger.

Here is a screenshot of what this initial setup should look like in Roblox Studio:

local module = {}
function Display(text)
local textLabel = script.Parent
textLabel.Text = text
module.Display = Display
return module
local DisplayTextModule = require(script.Parent.Parent.StarterGui.ScreenGui.OnScreenLogger.TextLabel.DisplayTextModuleScript)
DisplayTextModule.Display("hello, world")

The finished product will look like:


How to Change a Roblox Humanoid’s Appearance using Lua in Roblox Studio

I broke my femur skydiving a couple of weeks ago and am still laid up in a hospital bed recovering. I’ve been meaning to start learning a little Roblox development though, so I’m using this time lying in bed at the hospital to learn Roblox game development.

The first game that I want to make is a zombie game, because I think that’d be fairly simple to create. However, I found that I’ve been having some trouble doing two things:

  1. Detecting collisions between Humanoids
  2. Changing Humanoid’s Appearance (to turn them into zombies)

This quick blog post is just going to cover topic 2, changing humanoid’s appearance. I have a little code snippet that I created tonight that changes a Humanoid’s skin color to neon green so I can represent them as zombies. If you are looking to do something similar, maybe you’ll find this code snippet useful:

local Players = game:GetService("Players")
local function alterPlayer(player)
local character = player.Character or player.CharacterAdded:Wait()
local humanoid = character:WaitForChild("Humanoid")
local userId = player.UserId
local humanoidDescription = game.Players:GetHumanoidDescriptionFromUserId(userId)
humanoidDescription.HeadColor = Color3.fromHex("#39FF14")
humanoidDescription.LeftArmColor = Color3.fromHex("#39FF14")
humanoidDescription.RightArmColor = Color3.fromHex("#39FF14")
humanoidDescription.TorsoColor = Color3.fromHex("#39FF14")
humanoidDescription.LeftLegColor = Color3.fromHex("#39FF14")
humanoidDescription.RightLegColor = Color3.fromHex("#39FF14")
if humanoid then
local function onPlayerAdded(player)

Roblox Development Links

I’m laid up in the hospital right now with a broken femur (skydiving accident) and I’m trying to teach myself a little Roblox development. Roblox’s website has tons of great resources, but I don’t think it’s all that well organized. So I just wanted to write this really quick blog post to jot down the links that I have for getting started with Roblox development. Here are my links so far (will update as I learn more):

Roblox Docs (Use Slide Out Hamburger Menu):

Docs > Engine > Guides:

Docs > Engine > Tutorials:

Docs > Engine > Reference:

Docs > Engine > Resources:

Docs > Engine > Art:

Docs > Engine > Design:


Tutorials[Environmental Art]:

Docs > Engine > Guides > Coding Fundamentals:

And last, there is “Introduction to Scripting.” This is the best part of the docs in my opinion for learning how to build real Roblox games that use code. I had a hard time rediscovering this section, but here’s the link:


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Deploying Flask Apps to Production Linux Servers using Gunicorn and Nginx

This is is going to be a super short post that I’m really just writing for my own personal reference. The old guides that I used to use to setup my linux virtual machines for my flask apps keep giving me problems, so the purpose of this post is to jot down how to do this in the future the next time I need to do this.

First, reference this blog post: Deploy Flask The Easy Way With Gunicorn and Nginx!

What I like about this particular blog post is it skips all of the complicated pain in the @$$ steps like setting up non-root users and whatnot. I think using root is fine for small projects.

Last, the most critical thing is to make sure you install gunicorn into your virtual environment. When you do this, make sure to set the –ignore-installed flag so that gunicorn gets installed into the virtual environment. I believe this is the missing step from the previous guides I used to use which kept causing my setups to fail.

(venv) $ pip install --ignore-installed gunicorn

If you are installing from requirements.txt, also make sure to set the –ignore-installed flag so that gunicorn gets installed into your virtual environment instead of somewhere else:

(venv) $ pip install --ignore-installed -r requirements.txt


How to Switch Between Different Version of Cocoapods

Switching betweent different versions of cocoapods, I’ve been having to do this a lot at work recently. We have two branches of our codebase which are using different versions of cocoapods. At some point the all of the branches will end up using the same version of cocoapods, but at the moment one branch does not include the work which upgraded to the latest version of cocoapods. So if you find yourself in a similar situation, here’s all you have to do in order to switch between different versions.

First, uninstall cocoapods (the version which you don’t want to be using):

$ sudo gem uninstall cocoapods

Then, install the version you want to be using :

$ sudo gem install cocoapods -v 1.11.3

Feel free to switch back and forth between versions as needed.


Resolving Merge Conflicts in React Native: How to Address Conflicts in Pods, package-lock.json, yarn.lock, and project.pbxproj

Having trouble with merge conflicts in your React Native app with Pods, package-lock.json, yarn.lock, and project.pbxproj? I have the solution you’re looking for. These types of conflicts usually arise in React Native apps when one or both branches of code have installed a new node_module which uses native code, and then all sorts of conflicts will start to pop up in the Pods directory and project.pbxproj when you go to merge. The solution to fix these conflicts is to run $ pod deintegrate in both of your branches before doing your merge. This will take care of the majority of conflicts which tend to arise.

Then you’ll probably still have a few conflicts in package-lock.json, yarn.lock, and Podfile.lock. To fix the conflicts in package-lock.json or yarn.lock, you’ll want to checkout either branches package-lock.json or yarn.lock: $ git checkout name-of-your-branch — yarn.lock

For Podfile.lock, simply delete this file.

If there are any other conflicts which require manual resolution, go ahead and fix those. Then last, run $ pod install and then either $ npm install or $ yarn install. And boom! You’re back in business; merge conflicts resolved.

If you want to see every single terminal command from start to finish, please reference the 20 minute video above. Sometimes it’s hard to jot down every single step when it comes to doing something like this, so I find its helpful to just film everything for reference in case someone gets stuck on a particular step.