"A cannula is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of data"
Go Gopher designed by Renee French, original png created by Takuya Ueda licensed under CC 3.0 Attribution
Cannula is Go debug package that exposes debug information about your application to a unix socket. Currently it exposes the same data as "net/http/pprof" and "expvar". You can also register your own debug handlers to expose additional information and provide additional debug actions.
'net/http/pprof' registers its debug handlers with the default http ServeMux. This means that unless you have a proxy in front of your webserver blocking requests to /debug those handlers will be exposed to the internet. Cannula exposes the same data as net/http/pprof on a unix socket to make it much harder to accidentally expose your debug handlers to anything but localhost.
If you are using a recent version of curl (>= 7.40) you can use the --unix-socket to connect directly to the cannula socket. Otherwise you can use the cannula-proxy tool which creates a localhost proxy from an ephemeral tcp port to the unix socket. This is also how you can use go tool pprof directly against the running go application.
# List all debug handlers (requires curl >= 7.40)
curl --unix-socket /path/to/debug.sock 'http:/debug/'
# List all goroutine stacks (requires curl >= 7.40)
curl --unix-socket /path/to/debug.sock 'http:/debug/pprof/goroutine?debug=1'
# start cannula-proxy
cannula-proxy -addr 127.0.0.1:1337 /path/to/debug.sock &
# run a 5 second cpu profile
go tool pprof 'http://127.0.0.1:1337/debug/pprof/profile?seconds=5'
# run a heap profile
go tool pprof /path/to/server/binary http://127.0.0.1:1337/debug/pprof/heap
curl http://127.0.0.1:1337/debug/vars