2016-05-20 9:00
Setting up the New Relic agent is quite easy for a .wsgi application.
We have a pretty typical .wsgi file:
import os,sys
import newrelic.agent
newrelic.agent.initialize()
sys.stdout = sys.stderr
sys.path.append('/usr/local/lib/python2.7')
sys.path.append('/usr/local/lib/python2.7/site-packages')
os.environ['DJANGO_SETTINGS_MODULE'] = 'settings'
root_path = os.path.abspath(os.path.split(__file__)[0])
sys.path.insert(0, root_path)
from django.core.wsgi import get_wsgi_application
application = get_wsgi_application()
import newrelic.agent
newrelic.agent.initialize()
Two things to note here, first, the import and init of the agent must come first in the .wsgi file, otherwise the New Relic agent won't function properly. Now notice that the initialize() function is currently empty. This means the agent will initialize nothing and we won't see any reporting metrics in our New Relic dashboard.
Every time I deploy, I need to add the absolute path to the New Relic agent initializer in the .wsgi file. This tells the New Relic agent where to find the newrelic.ini file, which carries settings flags. I can’t check the path into the Git repo, because developer instances run the Django included runserver and the QA path is going to be different than the Production path.
[me@server application]$ l
total 60K
drwxrwxr-x. 8 me nginx 4.0K Apr 14 14:00 .
drwxrwsr-x. 14 nginx nginx 4.0K Mar 16 09:05 ..
lrwxrwxrwx 1 me me 28 Apr 14 14:00 current -> releases/2016.04.14_13.53.50
drwxrwxr-x. 8 me me 4.0K Mar 12 2015 .git
-rwxrwxr-x. 1 me me 72 Mar 12 2015 .gitignore
-rwxrwxr-x. 1 me me 448 Mar 12 2015 go
drwxrwxr-x. 2 me me 4.0K Apr 14 14:00 gobot
-rwxrwxr-x. 1 me me 562 Apr 14 13:45 go_config.json
drwxrwsr-x. 2 me nginx 4.0K May 18 04:00 logs
-rwxrwxr-x 1 me nginx 8.6K Mar 11 17:16 newrelic.ini
lrwxrwxrwx 1 me me 29 Apr 14 14:00 prev -> releases/2016.03.31_16.52.49/
-rwxrwxr-x. 1 me me 1.9K Mar 12 2015 README.md
drwxrwxr-x. 7 me nginx 4.0K Apr 14 13:53 releases
drwxrwxr-x. 3 me nginx 4.0K Mar 12 2015 .repositories
drwxrwxr-x. 3 me nginx 4.0K Mar 12 2015 shared
Here you can see that the newrelic.ini file currently lives in the parent directory as a sibling of the release directories. This isn't the best place to put it though, since our nifty little GoBot is already configured to symlink the shared directory across releases.
First, I want my newrelic.ini file to have deploy persistance, basically, I want it to always be available in the current directory.
Second, I want to keep track of what the file looked like on previous deploys. This would allow me to debug problems with the New Relic settings.
As it happens, our GoBot can handle both of these tasks. Basically, it will copy the newrelic.ini file from shared into current, switch the current symlink to the new release, then create a symlink in the new current to the original newrelic.ini file in shared. That file is never moving, but we are preserving the state of the file as it was when we are deploying new code. This will make it much easier to spot configuration drift if something goes wrong with New Relic.
Remember this line from before? newrelic.agent.initialize()?
We need to insert the path to newrelic.ini in the init function, like so: newrelic.agent.initialize('/path/to/newrelic.ini')
I need this path to be absolute, because it's the New Relic agent looking, not the Python process.
Turns out, I can reuse some Python code, with the sys library. Even better that I already have what I need in the .wsgi file!
sys.path[0]
This is pretty basic, but it outputs the first item in the sys.path list, which happens to be the absolute path to the current file.
In this case I get /var/www/vhosts/site/application and I need to append newrelic.ini.
So we'll put the newrelic.ini file in /shared after configuring GoBot to symlink it into /current.
Now our code should look like this:
import newrelic.agent
newrelic.agent.initialize(sys.path[0] + '/newrelic.ini')
The cool thing is, I can now check my .wsgi file into git and not worry about server configuration!