Custom Trace Resource
Inspektor Gadget uses a custom
Trace resource to communicate between the
endpoints and the
gadget DaemonSet running on the cluster. These
resources are used to control which gadgets run in a given cluster.
This is the basic format of this resource:
apiVersion: gadget.kinvolk.io/v1alpha1 kind: Trace metadata: name: trace-name namespace: gadget spec: node: node-name gadget: gadget-name filter: namespace: namespace-name podname: podname-name runMode: Manual outputMode: Status
Some gadgets work at the node level, while others support specific filters,
labels, and so on.
The possible values for
outputMode also depend on the gadget. The
seccomp gadget, for example, can create seccomp policies as an external
ExternalResource is selected. If
outputMode is set to
Status, the output of the trace will be stored in the status field of the
See the corresponding gadgets specs to find out what’s available.
Note that all traces should be created in the
gadget namespace. And,
for now, the node name needs to be explicitly set in the trace.
Trace resource is created, the
field is used to control when the gadget should run.
Some gadgets accept a single operation that triggers a run and stores the output. Other gadgets need to be started and stay running until they get stopped later on to obtain the output.
To control whether a gadget should get started or stopped, annotate the
corresponding trace resource with
Note that the trace controller will remove the annotation after it has
processed it. So, if you find yourself having to forcefully overwrite the
value of this field, it means that the trace controller is having trouble
Trace resources from the command line
It’s possible to create and interact with the
Trace resources directly
from the command line, using
kubectl apply with a YAML file containing
the specified trace.
After creating the resource, the corresponding operation can be set with
kubectl annotate, as in the following example:
kubectl annotate -n gadget trace/trace-name gadget.kinvolk.io/operation=start
Trace resources from graphical interfaces
Graphical interfaces that interact with Kubernetes, can integrate with
Inspektor Gadget by creating and modifying
Trace resources in the
gadget namespace, and following the corresponding gadget specifications.
Gadgets can then be controlled by annotating the
gadget.kinvolk.io/operation field with the corresponding operation.
As an example, see the biolatency plugin implementation for Headlamp.
Interacting with traces using the
kubectl-gadget plugin may create, annotate and delete
resources as necessary to interact with the
gadget DaemonSet running on
the nodes. This is mostly transparent to the user, who will just get the
results through the command-line.