Consider evolution:

* The developer creates the necessary containers by hand.

* The developer creates the necessary containers using previously prepared scripts.

* The system administrator, using any configuration and deployment management system, such as Chef, Pupel, Ansible, Salt, sets the topology of the system. The topology indicates which container is located in which place.

* Orchestration (schedulers) – semi-automatic distribution, maintenance of the state and reaction to system changes. For example: Google Kubernetes, Apache Mesos, Hashicorp Nomad, Docker Swarm mode, and YARN, which we'll cover. New ones also appear: Flocker , Helios .

There is a native Docker-swarm solution. Of the adult systems, Kubernetes (Kubernetes) and Mesos showed the most popularity, while the former is a universal and completely ready-to-use system, and the latter is a complex of various projects combined into a single package and allowing you to replace or change their components. There is also a huge number of less popular solutions that are not promoted by such giants as Google, Twitter and others: Nomad, Scheduling, Scalling, Upgrades, Service Descovery, but we will not consider them. Here we will consider the most ready-made solution – Kubernetes, which has gained great popularity for its low entry threshold, support and sufficient flexibility in most cases, pushing Mesos into the niche of customizable solutions when customization and development is economically justified.

Kubernetes has several ready-made configurations:

* MiniKube – a cluster of one local machine, designed to overcome the threshold of entry and experiments;

* kubeadm;

* kops;

* Kubernetes-Ansible;

* microKubernetes;

* OKD;

* MicroK8s.

To start the cluster yourself, you can use

KubeSai – Free Kubernetes

The smallest structural unit is called POD, which corresponds to the YML file in Docker-compose. The process of creating a POD, like other entities, is done declaratively: by writing or changing a configuration YML file and applying it to a cluster. And so, let's create a POD:

# test_pod.yml

# kybectl create -f test_pod.yaml

containers:

– name: test

image: debian

To run multiple replicas:

# test_replica_controller.yml

# kybectl create -f test_replica_controller.yml

apiVersion: v1

kind: ReplicationController

metadata:

name: Nginx

spec:

replicas: 3

selector:

app: Nginx // label by which the replica determines the presence of running containers

template:

containers:

– name: test

image: debian

For balancing, a type of service (logical entity) is used – LoadBalancer, in addition to which there is also ClasterIP and Node Port:

appVersion: v1

kind: Service

metadata:

name: test_service

apec:

type: LoadBalanser

ports:

– port: 80

– targetPort: 80

– protocol: TCP

– name: http

selector:

app: WEB

Overlay network plugins (created and configured automatically): Contig, Flannel, GCE networking, Linux bridging, Calico, Kube-DNS, SkyDNS. #configmap apiVersion: v1 kind: ConfigMap metadata: name: config_name data:

Similar to secrets in Docker-swarm, there is a secret for Kubernetes, an example of which can be NGINX settings:

#secrets

apiVersion: v1

kind: Secrets

metadata: name: test_secret

data:

password: ....

And to add a secret to POD, you need to specify it in the POD config:

....

valumes:

secret:

secretName: test_secret

…

Kubernetes has more flavors of Volumes:

* emptyDir;

* hostPatch;

* gcePersistentDisc – drive on Google Cloud;

* awsElasticBlockStore – A disk on Amazon AWS.

volumeMounts:

– name: app

nountPath: ""

volumes:

– name: app

hostPatch:

....

Feature for UI: Dashbord UI

Additionally available:

* Main metrics – collection of metrics;

* Logs collect – collecting logs;

* Scheduled JOBs;

* Autentification;

* Federation – distribution by data centers;

* Helm is a package manager similar to Docker Hub.

https://www.youtube.com/watch?v=FvlwBWvI-Zg

Docker commands

Docker is a more modern counterpart to RKT containers.

In Linux, when a process terminates with PID = 1, then NameSpace is also buried, which leads to the shutdown of the OS, in the case of a container, similarly, since it is a special case of the OS. The delimitation of processes in itself does not provide additional overhead, as well as monitoring and limiting resources for processes, because systemd provides the same configuration options in the host OS. Network virtualization occurs completely: both localhost and bridge, which allows you to create bridges from several containers to one localhost and thereby make it a single one for them, which is actively used in POD Kubernetes.