88 lines
4.2 KiB
Markdown
88 lines
4.2 KiB
Markdown
# Kubernetes Entrypoint
|
|
|
|
[](https://travis-ci.org/stackanetes/kubernetes-entrypoint)
|
|
[](https://quay.io/repository/stackanetes/kubernetes-entrypoint)
|
|
[](https://goreportcard.com/report/stackanetes/kubernetes-entrypoint)
|
|
|
|
|
|
============
|
|
|
|
Kubernetes-entrypoint enables complex deployments on top of Kubernetes.
|
|
|
|
## Overview
|
|
|
|
Kubernetes-entrypoint is meant to be used as a container entrypoint, which means it has to bundled in the container.
|
|
Before launching the desired application, the entrypoint verifies and waits for all specified dependencies to be met.
|
|
|
|
The Kubernetes-entrypoint queries directly the Kubernetes API and each container is self-aware of its dependencies and their states.
|
|
Therefore, no centralized orchestration layer is required to manage deployments and scenarios such as failure recovery or pod migration become easy.
|
|
|
|
## Usage
|
|
|
|
Kubernetes-entrypoint reads the dependencies out of environment variables passed into a container.
|
|
There is only one required environment variable "COMMAND" which specifies a command (arguments delimited by whitespace) which has to be executed when all dependencies are resolved:
|
|
|
|
`COMMAND="sleep inf"`
|
|
|
|
Kubernetes-entrypoint introduces a wide variety of dependencies which can be used to better orchestrate once deployment.
|
|
|
|
## Supported types of dependencies
|
|
|
|
All dependencies are passed as environement variables in format of `DEPENDENCY_<NAME>` delimited by colon. For dependencies to be effective please use [readiness probes](http://kubernetes.io/docs/user-guide/production-pods/#liveness-and-readiness-probes-aka-health-checks) for all containers.
|
|
|
|
### Service
|
|
Checks whether given kubernetes service has at least one endpoint.
|
|
Example:
|
|
|
|
`DEPENDENCY_SERVICE=mariadb,keystone-api`
|
|
|
|
### Container
|
|
Within a pod composed of multiple containers, it waits for the containers specified by their names to start.
|
|
This dependency requires a `POD_NAME` environement variable which can be easily passed through the [downward api](http://kubernetes.io/docs/user-guide/downward-api/).
|
|
Example:
|
|
|
|
`DEPENDENCY_CONTAINER=nova-libvirt,virtlogd`
|
|
|
|
### Daemonset
|
|
Checks if a specified daemonset is already running on the same host, this dependency requires a `POD_NAME`
|
|
env which can be easily passed through the [downward api](http://kubernetes.io/docs/user-guide/downward-api/).
|
|
The `POD_NAME` variable is mandatory and is used to resolve dependencies.
|
|
Example:
|
|
|
|
`DEPENDENCY_DAEMONSET=openvswitch-agent`
|
|
|
|
Simple example how to use downward API to get `POD_NAME` can be found [here](https://raw.githubusercontent.com/kubernetes/kubernetes.github.io/master/docs/user-guide/downward-api/dapi-pod.yaml).
|
|
|
|
### Job
|
|
Checks if a given job succeded at least once.
|
|
Example:
|
|
|
|
`DEPENDENCY_JOBS=nova-init,neutron-init`
|
|
|
|
### Config
|
|
This dependency performs a container level templating of configuration files. It can template an ip address `{{ .IP }}` and hostname `{{ .HOSTNAME }}`.
|
|
Templated config has to be stored in an arbitrary directory `/configmaps/<name_of_file>/<name_of_file>`.
|
|
This dependency requires `INTERFACE_NAME` environment variable to know which interface to use for obtain ip address.
|
|
Example:
|
|
|
|
`DEPENDENCY_CONFIG=/etc/nova/nova.conf`
|
|
|
|
The Kubernetes-entrypoint will look for the configuration file `/configmaps/nova.conf/nova.conf`, template
|
|
`{{ .IP }} and {{ .HOSTNAME }}` tags and save the file as `/etc/nova/nova.conf`.
|
|
|
|
### Socket
|
|
Checks whether a given file exists and container has rights to read it.
|
|
Example:
|
|
|
|
`DEPENDENCY_SOCKET=/var/run/openvswitch/ovs.socket`
|
|
|
|
## Image
|
|
|
|
Build process for image is trigged after each commit.
|
|
Can be found [here](https://quay.io/repository/stackanetes/kubernetes-entrypoint?tab=tags), and pulled by executing:
|
|
`docker pull quay.io/stackanetes/kubernetes-entrypoint:v0.1.0`
|
|
|
|
## Examples
|
|
|
|
[Stackanetes](http://github.com/stackanetes/stackanetes) uses kubernetes-entrypoint to manage dependencies when deploying OpenStack on Kubernetes.
|