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DLV Debugging of VCH servers

Overview

This notes describes how to set up dlv remote debugging of VCH servers

Building debug enabled binaries (non stripped)

Set the following environment variable to tell the Makefile to build non-stripped binaries:

export VIC_DEBUG_BUILD=true

Preparing the VCH for debugging

Ssh must be enabled on the VCH. To enabled it run the following command:

vic-machine-linux debug --target <TARGET> --thumbprint <THUMBPRINT> --name <vch-name> --enable-ssh --key <PATH-TO-AUTHORIZED-KEYS-FILE>

Both scripts: dlv-setup.sh and dlv-ctl.sh rely on ssh public-key authentication as specified by the command above (authorized_keys file).

The script dlv-setup.sh must be used to set up the VCH to run dlv. It performs several tasks:

  • opens the necessary ports in the iptables,
  • copies the GO environment necessary to run dlv (from $GOROOT and $GOPATH),
  • creates the attach and detach scripts that reside in /usr/local/bin in the VCH

The command requires the address (or FQDN) of the VCH. The environment variables:

DOCKER_HOST

or

DLV_TARGET_HOST

can be used to pass that information to dlv-setup.sh. Alternatively the option -h can be used on the command line. For instance:

dlv-setup.sh -h <target IP address/FQDN>

Launching dlv on the target host

To launch dlv and attach it to one of the VCH server run the command dlv-ctl.sh. The following target servers are supported:

  • vic-init
  • vic-admin
  • port-layer
  • docker-engine
  • vic-machine

The scripts needs the IP address (or the FQDN) of the target VCH host. The same environment variable and command line options as dlv-setup.sh are accepted. The script takes two arguments:

  • action: this can be either attach or detach
  • target: this can be one of the VCH services listed above For example:
dlv-ctl.sh -h <target IP address/FQDN> attach vic-admin

launches dlv in headless mode and attaches it to vic-admin and prints out the port number on which dlv listens. To detach you can use:

dlv-ctl.sh -h <target IP address/FQDN> detach vic-admin

The script allows specifying the action through with a couple of additional options -a (for attach) and -d for detach. The following example performs an attach:

dlv-ctl.sh -h <target IP address/FQDN> -a vic-admin

A detach can be performed by using:

dlv-ctl.sh -h <target IP address/FQDN> -d vic-admin

To view the DLV action logs from the VCH, the following command can be used

dlv-ctl.sh -h <target IP address/FQDN> log vic-admin

Similarly the option -l can be used.

Using Goland to perform remote debugging

After dlv is attached to the appropriate server, you can configure Goland to start debugging that process. On the drop down list with the debugger configurations select: Edit Configurations. In the configuration tab click on the + button to add a new configuration. Select Go Remote. Type in the the VCH IP address (or FQDN) and the port number returned by the dlv-ctl attach command. The debugger should be able to connect to the server.

Timeout issues while debugging

Consider for example the case in which a request is sent to the port-layer from docker-engine. When the request is received by the port-layer a breakpoint is hit. The developer next steps through the code in the port-layer while the docker-engine is waiting for a response. This may cause the docker-engine to timeout and abort or retry the request. Ideally when debugging is enabled all the timeouts should be increased to allow slower response times. This has not yet been implemented. The current idea is to connect the extension of timeout duration with the debug level specified at the time of VCH creation.

Debugging vic-machine

The target vic-machine has been added to debug the vic-machine remotely, in this case everything above applies with the exception that the vic-machine does not usually run on a VCH host.