herald

Herald

herald means a messanger.
It is a sample app to test pub/sub of backing emqx message broker
using elio library.

If you run skaffold with assets.k8s/skaffold.yaml,
it is configured as follows in a Kubernetes:

Prerequisites

Setting Skaffold on WSL

Setting up elio

Before start, set up elio project.

git clone https://github.com/cppis/elio && cd elio
go mod vendor
export ELIO_ROOT=$(pwd)

$ELIO_ROOT is the project root path.

Running app on Host

Using go run

To run herald service, run the following command:

HERALD_IN_URL="0.0.0.0:7002" go run app/herald

You can change the listening url of service herald by changing
environment variable HERALD_IN_URL.

Running app on Kubernetes

Create a Kind cluster

To create a kind, run the following command:

kind create cluster --config app/herald/assets.k8s/kind.cluster.yaml --name elio

To check if the kind cluster is up and running, run the following command:

kubectl config current-context
  kind-elio

Using the Helm

To deploy using helm, run the following command:

helm upgrade --install herald app/herald/assets.k8s/helm

Using the Kind+Skaffold

To run herald using Skaffold,
run the following command in the Project root directory:

skaffold -f app/herald/assets.k8s/skaffold.yaml dev -vdebug

To change detection triggered to manual mode, use option --trigger=manual.

Or, to run herald in debugging mode using Skaffold, run the following command:

skaffold -f app/herald/assets.k8s/skaffold.yaml debug

using Helm

cd $ELIO_ROOT
helm install herald .
helm uninstall herald

using Docker

docker build --no-cache -t localhost:5001/skaffold-herald:latest -f app/herald/assets.k8s/Dockerfile .
docker push localhost:5001/skaffold-herald:latest

Testing app

You can test echo easily by using telnet.

app protocol is custom t2p like http.
procotol header is separated by newline(\n or \r\n).
And packet delimiter is double newline(\n\n or \r\n\r\n).

connect: connect to echo using telnet

telnet localhost 7002

echo: echo message

echo<newline>
{message}<newline><newline>

sub: subcribe to topic

sub<newline>
{topic}<newline><newline>

unsub: unsubcribe from topic

unsub<newline>
{topic}<newline><newline>

pub: publish message to topic

pub<newline>
{topic}<newline>
{message}<newline><newline>

Debugging Tips

• Running telnet in Kubernetes:

kubectl run -it --rm --restart=Never busybox --image=gcr.io/google-containers/busybox -- sh

• Port forwarding a pod in Kubernetes:

kubectl port-forward $(kubectl get pods --selector=app=herald --output=jsonpath={.items..metadata.name}) 7002:7002

Ending app

Kubernetes resource cleanup

After running skaffold run or skaffold deploy and deploying your app to a cluster, running skaffold delete will remove all the resources you deployed. Cleanup is enabled by default, it can be turned off by --cleanup=false

Ctrl + C

When running skaffold dev or skaffold debug, pressing Ctrl+C (SIGINT signal) will kick off the cleanup process which will mimic the behavior of skaffold delete. If for some reason the Skaffold process was unable to catch the SIGINT signal, skaffold delete can always be run later to clean up the deployed Kubernetes resources.

To enable image pruning, you can run Skaffold with both --no-prune=false and --cache-artifacts=false:

skaffold dev --no-prune=false --cache-artifacts=false

Delete a Kind cluster

To delete a kind, run the following command:

kind delete cluster --name elio

Reference

• Building K8S cluster of EMQ X starting from scratch

TO-DO

• Run emqx as stateful cluster in kubernetes