Having trouble with the agent? Take a look here.
Below are some troubleshooting steps you can try. If you’re still having trouble, please contact us via email at firstname.lastname@example.org.
If you’re having issues setting up Skylight, run
skylight doctor in your production terminal. You should see something like this as the output:
Checking for Rails Rails application detected Checking for native agent Native agent installed Checking for valid configuration Configuration is invalid authentication token required
heroku run bash.
If you don’t see any helpful information after running
skylight doctor, be sure to check out the rest of our troubleshooting guide below.
Verify that the application is running with the correct Rails environment. By default, the agent only starts in the
production environment, but this can be configured.
To learn how to change what environments Skylight starts in, see Railtie Environments.
skylightgem in the right group?
Verify that, in your app’s
Gemfile, you’ve added the
skylight gem to a group that will be installed in production. For example, if you add
skylight to the
development group, it will not run when you deploy to production.
By default, Skylight uses your Rails tmp path as the sockfile directory. In the event that this path isn’t writable you should set
daemon.sockdir_path in your config.
Skylight’s socket file can’t be located on an NFS mount. Set
daemon.sockdir_path in your config to a non-NFS path.
To make sure Skylight is activated, you may need to restart your Unicorn masters.
You might see this bug if the agent running in your Rails app stops reporting performance data to Skylight. If you were able to see data before but it has stopped working recently, restarting your server will usually fix the issue.
If the agent encounters multiple errors in a short span of time, it will shut itself down. This is done out of an abundance of caution to ensure that a potential bug in the agent doesn’t bring down your app in production.
We are working to add more logging to the agent so we can better diagnose what causes the agent to shutdown and recover gracefully in the event of an error. If you find this is happening regularly, please let us know!
First, make sure that there is traffic to your application. If your Rails app is handling requests, you should start to see data in Skylight in just a few minutes.
We have received reports of problems running on the
cedar-10 stack. You should upgrade to the
If your app is running and has traffic, but you’re still not seeing anything in Skylight, verify that the
skylight gem is installed and running properly.
Make sure you are using the latest version of the Skylight gem. In the directory for your Rails app, run this command:
bundle list | grep skylight
You should see something like the following output:
* skylight (version number)
If the gem is installed and up-to-date, the next step is to verify that it is running correctly:
heroku logs -tto show the application log.
heroku restartto restart the app.
Keep an eye on the log terminal. If you see an error message stating that the Skylight agent is missing an authentication token, verify that you have configured Skylight in Heroku properly.
To avoid taking your production application down due to an installation failure, Skylight does not raise an exception when it can’t install the native agent. Currently, we support Linux 2.6.18+ and Mac OS X 10.8+. If you’re running a compatible OS and still see errors, try running your application with
SKYLIGHT_REQUIRED=true. This will cause Skylight to raise an exception when the native agent is missing. This exception may be useful in troubleshooting the problem. If you need help, send this to us at email@example.com.
This is actually a known bug, but it’s quite rare these days and we’ve had trouble reproducing it, so have had trouble fixing it. Please do email firstname.lastname@example.org and let us know exactly what steps you took when signing up, especially if there were any errors or issues along the way, or if you refreshed the invitation signup page at all before clicking “sign up with GitHub.” Any information about anything out of the ordinary helps!
In the meantime, you can ask the person who initially invited you to send another invitation to the email address associated with your account. This will add you to the app automatically and you should have no further issues.
There are a few reasons why this might happen.
Sorry, right now we only support repos that are connected to an organization, though we may allow use of personal repos in the future. Shoot us an email at email@example.com to let us know if this feature is important to you!
The Skylight agent will log errors to
log/skylight.log or on Heroku in STDOUT (Look for lines starting with
failed to instrument span; msg=native Trace#start_span failed
This error occurs when an event is too complex for Skylight’s agent to track. Here are a few potential causes for this issue:
internal error: failed to lex SQL query
These errors indicate that the agent is unable to parse a SQL query in your application. There errors won’t prevent your application from operating, though they will reduce the information that we can display in the UI for these queries. They will be displayed in the Event Sequence as simply “SQL”, not the full sanitized query.
Generally, the reason you will see this error is because you’re using a syntax we can’t recognize, often a more complex syntax or a non-standard syntax. For example, the agent doesn’t currently support square brackets allowed by MS SQL and Postgres. We’ve optimized for the most common syntax constructions and hope to support more in the future. When running across this error, please feel free to report it so we can learn what queries we’re failing to parse.
Memory profiler gems like
derailed generally use Ruby’s
ObjectSpace—a really nifty way to get information about all the objects allocated in your Ruby application that is great for troubleshooting memory issues.
Digging into the source of both
memory_profiler (which is used by derailed), we discovered the following line (source):
1file = ObjectSpace.allocation_sourcefile(obj)
This line looks at an object and asks
ObjectSpace who caused it to be allocated. As it turns out, objects allocated at require time are attributed to the file that calls the original
Now, this is all well and good except for one small problem: Skylight overwrites
Kernel#require in order to properly install probes. This means that it is Skylight that calls the original
Kernel#require, not whatever other gem is really doing the require. So, as soon as Skylight is loaded, every future
require call is attributed to Skylight.
Skylight isn’t the only library to do this. ActiveSupport has a similar hook in it’s
Loadable module that is included into
Object. Without Skylight, it would be ActiveSupport taking the blame. However, because this hook uses
super, it calls to the superclass
Kernel that is now the version that Skylight created.
So there you have it, run
derailed without Bundler and you’ll see RubyGems blamed for your requires. Add in Bundler and the correct files will get blamed. Bring in ActiveSupport and then ActiveSupport will be blamed. Include Skylight and blame will shift to us. Good times!
So what’s the moral here? Know your tools.
ObjectSpace and the libraries that use it do some really useful things. They aren’t perfect, but they’re open source. Read the code and find out a bit about how they work and you’ll be able to put them to better use!
Skylight performs setup when the gem is required, at which time Rails will be detected and tapped into. However, you may find you have to manually require
skylight/railtie if you need to load the Skylight gem before Rails.