Kubernetes service dependencies ready checker

when you create resources in kubernetes often yours containers failed to start because they need somes already running resources before starting. For example you deploy a php website and it must connect to a MySQL server. With kubernetes service dependencies embeded in the deployment, the container doesn't start until his all dependencies are ready

How it work

kubernetes service dependencies use "initContainers" mechanism of kubernetes. You can see the sample examples/helloworld.json.

This sample is helloworld waiting a ready mongodb instance before to start.

Releases

• 1.13.3 (unmaintened)
  • This version is supported kubernetes v1.13.3
• 1.15.0 (unmaintened)
  • This version is supported kubernetes v1.15.0
• 1.16 (unmaintened)
  • This version is supported kubernetes v1.15
• 1.17.5 (unmaintened)
  • This version is supported kubernetes v1.17
• 1.18.2 (unmaintened)
  • This version is supported kubernetes v1.18
• 1.20.5
  • This version is supported kubernetes v1.20
• 1.21.0
  • This version is supported kubernetes v1.21

How to use?

When you create kubernetes resources, just add an init container belong to your container.

"spec": {
    "initContainers": [
        {
            "image": "fred78290/kubernetes-svc-dependencies:v1.20.5",
            "command": [
                "/usr/local/bin/check-dependencies"
            ],
            "args": [
                "-v",
                "--namespace=kube-public",
                "--kubeconfig=/etc/kubernetes/config",
                "--maxretry=5",
                "--sleep=15",
                "--timeout=300",
                "svc/kube-public:mongodb"
            ],
            "name": "helloworld-init",
            "volumeMounts": [
                {
                    "name": "kubeconfig",
                    "mountPath": "/etc/kubernetes/config",
                    "readOnly": true
                }
            ]
        }
    ],
    "containers": [
        ...
    ],
    "volumes": [
        {
            "name": "kubeconfig",
            "hostPath": {
                "path": "/etc/kubernetes/admin.conf",
                "type": "File"
            }
        }
    ]
}

Command line arguments

Name	Description
-n | --namespace	Default namespace
-k | --kubeconfig	Kubeconfig file
-a | --apiserver	apiserver host
-r | --maxretry	The number of retry before a dependency is considered as unready
-b | --keeponerror	Try always to reach the dependency else the process exit
-i | --ignoreerror	Ignore error
-v | --verbose	Verbose
-s | --sleep	Time interval in time.Duration unit
-t | --timeout	Time to wait before to declare service down in time.Duration unit
dependencies	Enumeration of dependencies

Syntax to enumerate dependencies

The dependency is composed of 3 parts: type of kubernetes resource, namespace and resource name. The syntax is < resource >/< namespace >:< name >

Resource	Description	Example
po	Pod	po/kube-public:mongodb-023a4
deploy	Deployment	deploy/kube-public:mongodb
ds	DaemonSet	ds/kube-public:mongodb
rs	Replicaset	rs/kube-public:mongodb
rc	Replication controller	rc/kube-public:mongodb
sts	Statefulset	sts/kube-public:mongodb
svc	Service	svc/kube-public:mongodb

Build

To build the docker image, enter make container