Peterbe.com

tl;dr; Here's a useful bash script to avoid starting something when its already running as a ghost process.

Huey is a great little Python library for doing background tasks. It's like Celery but much lighter, faster, and easier to understand.

What cost me almost an hour of hair-tearing debugging today was that I didn't realize that a huey daemon process had gotten stuck in the background with code that wasn't updating as I made changes to the tasks.py file in my project. I just couldn't understand what was going on.

The way I start my project is with honcho which is a Python Foreman clone. The Procfile looks something like this:

elasticsearch: cd /Users/peterbe/dev/PETERBECOM/elasticsearch-7.7.0 && ./bin/elasticsearch -q
web: ./bin/run.sh web
minimalcss: cd minimalcss && PORT=5000 yarn run start
huey: ./manage.py run_huey --flush-locks --huey-verbose
adminui: cd adminui && yarn start
pulse: cd pulse && yarn run dev

And you start that with simply typing:

honcho start

When you Ctrl-C, it kills all those processes but somehow somewhere it doesn't always kill everything. Restarting the computer isn't a fun alternative.

So, to prevent my sanity from draining I wrote this script:

#!/usr/bin/env bash
set -eo pipefail

# This is used to make sure that before you start huey, 
# there isn't already one running the background.
# It has happened that huey gets lingering stuck as a 
# ghost and it's hard to notice it sitting there 
# lurking and being weird.

bad() {
    echo "Huey is already running!"
    exit 1
}

good() {
    echo "Huey is NOT already running"
    exit 0
}

ps aux | rg huey | rg -v 'rg huey' | rg -v 'huey-isnt-running.sh' && bad || good

(If you're wondering what rg is; it's short for ripgrep)

And I change my Procfile accordingly:

-huey: ./manage.py run_huey --flush-locks --huey-verbose
+huey: ./bin/huey-isnt-running.sh && ./manage.py run_huey --flush-locks --huey-verbose

There really isn't much rocket science or brain surgery about this blog post but I hope it inspires someone who's been in similar trenches that a simple bash script can make all the difference.

I knew I didn't want to download the sources to nginx to install it on my new Ubuntu 19.10 server because I'll never have the discipline to remember to keep it upgraded. No, I'd rather just run apt update && apt upgrade every now and then.

Why is this so hard?! All I need is the ability to set brotli_static on; in my Nginx config so it'll automatically pick the .br file if it exists on disk.

These instructions totally helped but here they are specifically for my version (all run as root):

git clone --recursive https://github.com/google/ngx_brotli.git

apt install brotli
apt-get build-dep nginx

# Note the version of which nginx you have installed
nginx -v
# ...which informs which URL to wget
wget https://nginx.org/download/nginx-1.17.9.tar.gz
aunpack nginx-1.17.9.tar.gz
nginx -V 2>&1 >/dev/null | grep -o " --.*" | grep -oP .+?(?=--add-dynamic-module)| head -1 > nginx-1.17.9/build_args.txt
cd nginx-1.17.9/
./configure --with-compat $(cat build_args.txt) --add-dynamic-module=../ngx_brotli
make install

cp objs/ngx_http_brotli_filter_module.so  /usr/lib/nginx/modules/
chmod 644 /usr/lib/nginx/modules/ngx_http_brotli_filter_module.so
cp objs/ngx_http_brotli_static_module.so /usr/lib/nginx/modules/
chmod 644 /usr/lib/nginx/modules/ngx_http_brotli_static_module.so

ls -l /etc/nginx/modules

Now I can edit my /etc/nginx/nginx.conf (somewhere near the top) to:

load_module /usr/lib/nginx/modules/ngx_http_brotli_filter_module.so;
load_module /usr/lib/nginx/modules/ngx_http_brotli_static_module.so;

And test that it works:

nginx -t

I'm setting up a new Ubuntu (Eoan Ermine) 19.10 server and I noticed that apt install nodejs gives you Node v10 which is an LTS (Long Term Support) version that'll last till April 2021. However, I want Node v12 which is the most recent LTS release as of April 2020.

To install it I used these instructions:

curl -sL https://deb.nodesource.com/setup_12.x | sudo -E bash -
sudo apt-get install -y nodejs

That worked great.
When it finished, it spat out this nice little blurb about how to install yarn:

...
Fetched 7454 B in 1s (12.3 kB/s)
Reading package lists... Done

## Run `sudo apt-get install -y nodejs` to install Node.js 12.x and npm
## You may also need development tools to build native addons:
     sudo apt-get install gcc g++ make
## To install the Yarn package manager, run:
     curl -sL https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
     echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
     sudo apt-get update && sudo apt-get install yarn

By the way, I have no idea what nodejs-mozilla but running apt show nodejs-mozilla yields:

Package: nodejs-mozilla
Version: 12.16.1-0ubuntu0.19.10.1
Priority: optional
Section: universe/javascript
Origin: Ubuntu
Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 42.0 MB
Depends: libc6 (>= 2.29), libgcc1 (>= 1:3.4), libstdc++6 (>= 9)
Homepage: http://nodejs.org/
Download-Size: 10.4 MB
APT-Sources: http://mirrors.digitalocean.com/ubuntu eoan-updates/universe amd64 Packages
Description: evented I/O for V8 javascript
 Node.js is a platform built on Chrome's JavaScript runtime for easily
 building fast, scalable network applications. Node.js uses an
 event-driven, non-blocking I/O model that makes it lightweight and
 efficient, perfect for data-intensive real-time applications that run
 across distributed devices.
 .
 Node.js is bundled with several useful libraries to handle server
 tasks:
 .
 System, Events, Standard I/O, Modules, Timers, Child Processes, POSIX,
 HTTP, Multipart Parsing, TCP, DNS, Assert, Path, URL, Query Strings.

Installing it doesn't add a node executable and I can't find a home page for it. apt can be weird sometimes.

Instead of upgrading everything on my server, I'm just starting from scratch. From Ubuntu 16.04 to Ubuntu 19.04 and I also upgraded everything else in sight. One of them was uwsgi. I copied various user config files but for uwsgi things didn't very well. On the old server I had uwsgi version 2.0.12-debian and on the new one 2.0.18-debian. The uWSGI changelog is pretty hard to read but I sure don't see any mention of this.

You see, on SongSearch I have it so that Nginx talks to Django via a uWSGI socket. But the NodeJS server talks to Django via 127.0.0.1:PORT. So I need my uWSGI config to start both. Here was the old config:

[uwsgi]
plugins = python35
virtualenv = /var/lib/django/songsearch/venv
pythonpath = /var/lib/django/songsearch
user = django
uid = django
master = true
processes = 3
enable-threads = true
touch-reload = /var/lib/django/songsearch/uwsgi-reload.touch
http = 127.0.0.1:9090
module = songsearch.wsgi:application
env = LANG=en_US.utf8
env = LC_ALL=en_US.UTF-8
env = LC_LANG=en_US.UTF-8

(The only difference on the new server was the python37 plugin instead)

I start it and everything looks fine. No errors in the log files. And netstat looks like this:

# netstat -ntpl | grep 9090
tcp        0      0 127.0.0.1:9090          0.0.0.0:*               LISTEN      1855/uwsgi

But every time I try to curl localhost:9090 I kept getting curl: (52) Empty reply from server. Nothing in the log files! It seemed no matter what I tried I just couldn't talk to it over HTTP. No, I'm not a sysadmin. I'm just a hobbyist trying to stand up my little server with the tools and limited techniques I know but I was stumped.

The solution

After endless Googling for a resolution and trying all sorts of uwsgi commands directly, I somehow stumbled on the solution.

[uwsgi]
plugins = python35
virtualenv = /var/lib/django/songsearch/venv
pythonpath = /var/lib/django/songsearch
user = django
uid = django
master = true
processes = 3
enable-threads = true
touch-reload = /var/lib/django/songsearch/uwsgi-reload.touch
-http = 127.0.0.1:9090
+http-socket = 127.0.0.1:9090
module = songsearch.wsgi:application
env = LANG=en_US.utf8
env = LC_ALL=en_US.UTF-8
env = LC_LANG=en_US.UTF-8

With this one subtle change, I can now curl localhost:9090 and I still have the /var/run/uwsgi/app/songsearch/socket socket. So, yay!

I'm blogging about this in case someone else ever gets stuck in the same nasty surprise as me.

Also, I have to admit, I was fuming with rage from this frustration. It's really inspired me to revive the quest for an alternative to uwsgi because I'm not sure it's that great anymore. There are new alternatives such as gunicorn, gunicorn with Meinheld, bjoern etc.

I have Nginx 1.15.8 installed with Homebrew on my macOS. By default the /usr/local/etc/nginx/nginx.conf it set to...:

worker_processes  1;

But, from the documentation, it says:

"The optimal value depends on many factors including (but not limited to) the number of CPU cores, the number of hard disk drives that store data, and load pattern. When one is in doubt, setting it to the number of available CPU cores would be a good start (the value “auto” will try to autodetect it)." (bold emphasis mine)

What is the ideal number for me? The performance of Nginx on my laptop doesn't really matter. But for my side-projects it's important to have a fast Nginx since it serves static HTML and lots of static assets. However, on my personal servers I have a bunch of other resource hungry stuff going on that I know is more likely to need the resources, like Elasticsearch and uwsgi.

To figure this out, I wrote a benchmark program that requested a small index.html about 10,000 times across 10 concurrent clients with hey.

hey -n 10000 -c 10 http://peterbecom.local/plog/variable_cache_control/awspa

I ran this 10 times between changing the worker_processes in the nginx.conf file. Here's the output:

1 WORKER PROCESSES
BEST  : 13,607.24 reqs/s

2 WORKER PROCESSES
BEST  : 17,422.76 reqs/s

3 WORKER PROCESSES
BEST  : 18,886.60 reqs/s

4 WORKER PROCESSES
BEST  : 19,417.35 reqs/s

5 WORKER PROCESSES
BEST  : 19,094.18 reqs/s

6 WORKER PROCESSES
BEST  : 19,855.32 reqs/s

7 WORKER PROCESSES
BEST  : 19,824.86 reqs/s

8 WORKER PROCESSES
BEST  : 20,118.25 reqs/s

Or, as a graph:

Now note, this is done here on my MacBook Pro. Not on my Ubuntu DigitalOcean servers. For now, I just want to get a feeling for how these numbers correlate.

Conclusion

The benchmark isn't good enough. The numbers are pretty stable but I'm doing this on my laptop with multiple browsers idling, Slack, and Spotify running. Clearly, the throughput goes up a bit when you allocate more workers but if anything can be learned from this, start with going beyond 1 for a quick fix and from there start poking and more exhaustive benchmarks. And don't forget, if you have time to go deeper on this, to look at the combination of worker_connections and worker_processes.

Suppose you have a cleartext file that you want to encrypt with a password, here's how you do that with ccrypt on macOS. First:

▶ brew install ccrypt

Now, you have the ccrypt program. Let's test it:

▶ cat secrets.txt
Garage pin: 123456
Favorite kid: bart
Wedding ring order no: 98c4de910X

▶ ccrypt secrets.txt
Enter encryption key: ▉▉▉▉▉▉▉▉▉▉▉
Enter encryption key: (repeat) ▉▉▉▉▉▉▉▉▉▉▉

# Note that the original 'secrets.txt' is replaced 
# with the '.cpt' version.
▶ ls | grep secrets
secrets.txt.cpt

▶ less secrets.txt.cpt
"secrets.txt.cpt" may be a binary file.  See it anyway?

There. Now you can back up that file on Dropbox or whatever and not have to worry about anybody being able to open it without your password. To read it again:

▶ ccrypt --decrypt --cat secrets.txt.cpt
Enter decryption key: ▉▉▉▉▉▉▉▉▉▉▉
Garage pin: 123456
Favorite kid: bart
Wedding ring order no: 98c4de910X

▶ ls | grep secrets
secrets.txt.cpt

Or, to edit it you can do these steps:

▶ ccrypt --decrypt secrets.txt.cpt
Enter decryption key: ▉▉▉▉▉▉▉▉▉▉▉


▶ vi secrets.txt

▶ ccrypt secrets.txt
Enter encryption key:
Enter encryption key: (repeat)

Clunky that you have you extract the file and remember to encrypt it back again. That's where you can use emacs. Assuming you have emacs already installed and you have a ~/.emacs file. Add these lines to your ~/.emacs:

(setq auto-mode-alist
 (append '(("\\.cpt$" . sensitive-mode))
               auto-mode-alist))
(add-hook 'sensitive-mode (lambda () (auto-save-mode nil)))
(setq load-path (cons "/usr/local/share/emacs/site-lisp/ccrypt" load-path))
(require 'ps-ccrypt "ps-ccrypt.el")

By the way, how did I know that the load path should be /usr/local/share/emacs/site-lisp/ccrypt? I looked at the output from brew:

▶ brew info ccrypt
ccrypt: stable 1.11 (bottled)
Encrypt and decrypt files and streams
...
==> Caveats
Emacs Lisp files have been installed to:
  /usr/local/share/emacs/site-lisp/ccrypt
...

Anyway, now I can use emacs to open the secrets.txt.cpt file and it will automatically handle the password stuff:

About to open

Opening with password

Opened

This is really convenient. Now you can open an encrypted file, type in your password, and it will take care of encrypting it for you when you're done (saving the file).

Be warned! I'm not an expert at either emacs or encryption so just be careful and if you get nervous take precaution and set aside more time to study this deeper.