A service is defined and deployed using a configuration file written in YAML
(YAML Ain't Markup Language). The deployment is defined in a declarative
style where the end state is specified and K8s does its best to maintain this
state. For example, you can define a service where the deployment must have
eight Pods running at all times across the cluster. If a Pod fails, K8s will do its
best to schedule another Pod to maintain the defined end state of the deploy-
ment (i.e., eight running Pods). The K8s master node will also try to schedule
Pods on worker nodes as efficiently as possible across the cluster, ensuring
even load distribution and resiliency.
Kubernetes Master
API Server
Controller Manager
Users
Scheduler
Developer
/ Operator
etcd
Kubelet
cAdvisor
Pod
Pod
Kube-Proxy
...
Pod
Kubelet
...
Pod
cAdvisor
Pod
Kube-Proxy
...
Pod
Plugin Network (e.g. Flannel, Weavenet, etc.)
Kubernetes Node
Kubernetes Node
Figure 3: Kubernetes architecture
Helm
So we have identified a system for solving the problem of automatically sched-
uling and ensuring resiliency in this distributed cluster, but how would you
describe the application you want to deploy? You can imagine that the YAML
configuration can get rather complex, even for a relatively simple website like
the Sock Shop where you need to specify ConfigMaps, services, Pods, per-
sistent volumes, etc. This is where Helm comes in. Think of Helm as a package
manager for K8s, analogous to what yum and apt are to Linux. Similarly, Helm
Charts are K8s packages analogous to debs and rpms. Helm gives developers a
way to package their entire application into Charts, which can be installed on
a K8s cluster with a single command. Not only does Helm give you an effective
package manager for K8s, but it also is a way to package and publish your appli-
cations to public repositories for others to leverage. Developers can find hun-
dreds of curated and stable Charts, packaging a variety of useful applications
ranging from databases (MySQL, MongoDB) to Web publishing applications,
such as WordPress.
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