Extend Chaos Daemon Interface

In Add new chaos experiment type, you have added HelloWorldChaos, which can print Hello World! in the logs of Chaos Controller Manager. To enable the HelloWorldChaos to inject some faults into the target Pod, you need to extend interface for Chaos Daemon.

It’s recommended to read Chaos Mesh architecture before you go forward. :::

This document covers:

Selector
Implement the gRPC interface
Verify the experiment

Selector

In api/v1alpha1/helloworldchaos_type.go, you have defined HelloWorldSpec, which includes ContainerSelector:

// HelloWorldChaosSpec is the content of the specification for a HelloWorldChaos
type HelloWorldChaosSpec struct {
    // ContainerSelector specifies target
    ContainerSelector `json:",inline"`
    // Duration represents the duration of the chaos action
    // +optional
    Duration *string `json:"duration,omitempty"`
}
...
// GetSelectorSpecs is a getter for selectors
func (obj *HelloWorldChaos) GetSelectorSpecs() map[string]interface{} {
    return map[string]interface{}{
        ".": &obj.Spec.ContainerSelector,
    }
}

In Chaos Mesh, Selector is used to define the scope of a chaos experiment, the target namespace, annotation, label, etc. Selector can also be some more specific values (for example, AWSSelector in AWSChaos). Usually, each chaos experiment requires only one Selector, with exceptions such as NetworkChaos because it sometimes needs two Selectors as two objects for network partition.

Implement the gRPC interface

To allow Chaos Daemon to accept the requests from Chaos Controller Manager, you need to implement a new gRPC interface.

Add the RPC in pkg/chaosdaemon/pb/chaosdaemon.proto:

service chaosDaemon {
   ...
   rpc ExecHelloWorldChaos(ExecHelloWorldRequest) returns (google.protobuf.Empty) {}
}
message ExecHelloWorldRequest {
   string container_id = 1;
}

You need to update the Golang code generated by this proto file:

make proto

Implement gRPC services in Chaos Daemon.

In the pkg/chaosdaemon directory, create a file named helloworld_server.go with the following contents:

package chaosdaemon
import (
"context"
"fmt"
"github.com/golang/protobuf/ptypes/empty"
"github.com/chaos-mesh/chaos-mesh/pkg/bpm"
pb "github.com/chaos-mesh/chaos-mesh/pkg/chaosdaemon/pb"
)
func (s *DaemonServer) ExecHelloWorldChaos(ctx context.Context, req *pb.ExecHelloWorldRequest) (*empty.Empty, error) {
log.Info("ExecHelloWorldChaos", "request", req)
pid, err := s.crClient.GetPidFromContainerID(ctx, req.ContainerId)
if err != nil {
    return nil, err
}
cmd := bpm.DefaultProcessBuilder("sh", "-c", fmt.Sprintf("ps aux")).
    SetNS(pid, bpm.MountNS).
    SetContext(ctx).
    Build()
out, err := cmd.Output()
if err != nil {
    return nil, err
}
if len(out) != 0 {
    log.Info("cmd output", "output", string(out))
}
return &empty.Empty{}, nil
}

After chaos-daemon receives the ExecHelloWorldChaos request, you can see a list of processes in the current container.

Send a gRPC request when applying the chaos experiment.

Each chaos experiment has its life cycle: apply and then recover. However, there are some chaos experiments that cannot be recovered by default (for example, PodKill in PodChaos, and HelloWorldChaos). These are called OneShot experiments. You can find +chaos-mesh:oneshot=true in the file that defines the schema type of chaos experiment type.

Chaos Controller Manager needs to send a request to Chaos Daemon when HelloWorldChaos is in recover. To do this, you need to modify controllers/chaosimpl/helloordchaos/types.go:

package helloworldchaos
import (
"context"
"github.com/chaos-mesh/chaos-mesh/api/v1alpha1"
"github.com/chaos-mesh/chaos-mesh/controllers/chaosimpl/utils"
"github.com/chaos-mesh/chaos-mesh/controllers/common"
"github.com/chaos-mesh/chaos-mesh/pkg/chaosdaemon/pb"
"github.com/go-logr/logr"
"go.uber.org/fx"
"sigs.k8s.io/controller-runtime/pkg/client"
)
type Impl struct {
client.Client
Log     logr.Logger
decoder *utils.ContainerRecordDecoder
}
// This corresponds to the Apply phase of HelloWorldChaos. The execution of HelloWorldChaos will be triggered.
func (impl *Impl) Apply(ctx context.Context, index int, records []*v1alpha1.Record, obj v1alpha1.InnerObject) (v1alpha1.Phase, error) {
impl.Log.Info("Apply helloworld chaos")
decodedContainer, err := impl.decoder.DecodeContainerRecord(ctx, records[index])
if err != nil {
    return v1alpha1.NotInjected, err
}
pbClient := decodedContainer.PbClient
containerId := decodedContainer.ContainerId
_, err = pbClient.ExecHelloWorldChaos(ctx, &pb.ExecHelloWorldRequest{
    ContainerId: containerId,
})
if err != nil {
    return v1alpha1.NotInjected, err
}
return v1alpha1.Injected, nil
}
// This corresponds to the Recover phase of HelloWorldChaos. The reconciler will be triggered to recover the chaos action.
func (impl *Impl) Recover(ctx context.Context, index int, records []*v1alpha1.Record, obj v1alpha1.InnerObject) (v1alpha1.Phase, error) {
impl.Log.Info("Recover helloworld chaos")
return v1alpha1.NotInjected, nil
}
func NewImpl(c client.Client, log logr.Logger, decoder *utils.ContainerRecordDecoder) *common.ChaosImplPair {
return &common.ChaosImplPair{
    Name:   "helloworldchaos",
    Object: &v1alpha1.HelloWorldChaos{},
    Impl: &Impl{
        Client:  c,
        Log:     log.WithName("helloworldchaos"),
        decoder: decoder,
    },
    ObjectList: &v1alpha1.HelloWorldChaosList{},
}
}
var Module = fx.Provide(
fx.Annotated{
    Group:  "impl",
    Target: NewImpl,
},
)

:::note In this chaos experiment, there is no need to recover the chaos action. This is because HelloWorldChaos is a OneShot experiment. For the chaos experiment type you developed, you can implement the logic of the recovery function as needed. :::

Verify the experiment

To verify the experiment, perform the following steps.

Build the Docker image and push it to your local Registry. If the Kubernetes cluster is deployed using kind, you need to load the image to kind:

make image
make docker-push
kind load docker-image localhost:5000/pingcap/chaos-mesh:latest
kind load docker-image localhost:5000/pingcap/chaos-daemon:latest
kind load docker-image localhost:5000/pingcap/chaos-dashboard:latest

Update Chaos Mesh:

Deploy the target Pod for testing. Skip this step if you have already deployed this Pod:

kubectl apply -f https://raw.githubusercontent.com/chaos-mesh/apps/master/ping/busybox-statefulset.yaml

Create a new YAML file with the following content:

apiVersion: chaos-mesh.org/v1alpha1
kind: HelloWorldChaos
metadata:
  name: busybox-helloworld-chaos
spec:
  selector:
    namespaces:
      - busybox
  mode: all
  duration: 1h

Apply the chaos experiment:

kubectl apply -f /path/to/helloworld.yaml

Verify the results. You can check several logs:

Check the logs of Chaos Controller Manager:

kubectl logs chaos-controller-manager-{pod-post-fix} -n chaos-testing

Example output:

2021-06-25T06:02:12.754Z        INFO    records apply chaos     {"id": "busybox/busybox-1/busybox"}
2021-06-25T06:02:12.754Z        INFO    helloworldchaos Apply helloworld chaos

Check the logs of Chaos Daemon:

kubectl logs chaos-daemon-{pod-post-fix} -n chaos-testing

Example output:

2021-06-25T06:25:13.048Z        INFO    chaos-daemon-server     ExecHelloWorldChaos     {"request": "container_id:\"containerd://af1b99df3513c49c4cab4f12e468ed1d7a274fe53722bd883256d8f65bc9f681\""}
2021-06-25T06:25:13.050Z        INFO    background-process-manager      build command   {"command": "/usr/local/bin/nsexec -m /proc/243383/ns/mnt -- sh -c ps aux"}
2021-06-25T06:25:13.056Z        INFO    chaos-daemon-server     cmd output      {"output": "PID   USER     TIME  COMMAND\n    1 root      0:00 sleep 3600\n"}
2021-06-25T06:25:13.070Z        INFO    chaos-daemon-server     ExecHelloWorldChaos     {"request": "container_id:\"containerd://88f6a469e5da82b48dc1190de07a2641b793df1f4e543a5958e448119d1bec11\""}
2021-06-25T06:25:13.072Z        INFO    background-process-manager      build command   {"command": "/usr/local/bin/nsexec -m /proc/243479/ns/mnt -- sh -c ps aux"}
2021-06-25T06:25:13.076Z        INFO    chaos-daemon-server     cmd output      {"output": "PID   USER     TIME  COMMAND\n    1 root      0:00 sleep 3600\n"}

You can see ps aux in two separate lines, which are corresponding to two different Pods.

:::note If your cluster has multiple nodes, you will find more than one Chaos Daemon Pod. Try to check logs of every Chaos Daemon Pods and find which Pod is being called. :::

Next steps

If you encounter any problems in this process, create an issue in the Chaos Mesh repository.

If you are curious about how all of these come into effect, you can read the README files of different controllers in the controller directory to learn their functionalities. For example, controllers/common/README.md.

Now you are ready to become a Chaos Mesh developer! You are welcome to visit the Chaos Mesh repository to find a good first issue and get started!