While serverless programming typically requires less code, that often comes at the cost of less visibility into the execution of that code. This page describes some troubleshooting tips for each FaaS runtime that can help as you create new functions.
Every time a function executes on OpenWhisk, it creates what OpenWhisk calls an activation record. The wsk CLI has a command that can list these records:
$ wsk activation list -i
activations
91a4008d07c241f7a4008d07c2d1f727 list
88661ee28df64b4fa61ee28df6ab4fe9 list
a31db224b4c448069db224b4c4b8067f list
6cae54737b994ea7ae54737b99aea7a3 create
1e1bcbe4d1db4e999bcbe4d1dbfe995a greeting
6c9e0c4f8b364bec9e0c4f8b36dbecec greeting
3bf2bb5af8574949b2bb5af85739493a greeting
4fb7cb304b994a3db7cb304b994a3da6 greeting
51ddf357f87748719df357f877c87140 greeting
492dc252c8f9404aadc252c8f9004a68 greetingand view the contents of an individual record:
$ wsk activation logs 91a4008d07c241f7a4008d07c2d1f727 -i
2018-08-16T15:04:28.215869463Z stdout: About to connect to:mongodb://fonkdb-mongodb.default:27017/guestbook_appWhen a function writes to stdout or stderr, the results show up here in the activation record. The example above came from the development of the Node.js Guestbook for OpenWhisk and shows a since removed console.log() of the MongoDB connection URL. Note that it sometimes takes a few minutes after the invocation of a function in order for its activation record to show up in the list.
The OpenFaaS Troubleshooting Guide provides many steps for interrogating an instance of OpenFaaS, including obtaining log data from function executions.
The Kubeless Debugging Guide offers a variety of tips for how to figure out what is going on inside functions.
Digging through the Fission CLI help system reveals how to inspect logs from a function invocation, but for convienence here is the command:
fission fn logs --name <function name>Keep in mind that there can be a delay between function invocation time and the log data becoming available.