However, Kubernetes also provides for namespacing and use of Fully Qualified Domain Names (FQDN). Like Docker Swarm, Kubernetes services may be referenced by its simple service name. Kubernetes provides numerous additional means to reference Pods and services through metadata, such as labels and annotations. Thus, Pods within a service can communicate by IP address, too. Each Pod and service receive an IP address relative to its parent. Kubernetes service domains are maintained by the KubeDNS Pod. Direct calls to containers can be achieved by using the container alias as the domain or by using the containers assigned IP address. In order to separate connectivity between services, each service can belong to one or more overlay networks. Each service host domain name is equivalent to the provided service name.
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Docker Swarm utilises a DNS service integrated within the Docker Engine.
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Service Discoveryīoth Docker Swarm and Kubernetes provide DNS based service discovery. As such, the decision to choose Kubernetes over Docker Swarm might be relevant when building applications that require fine tuning in order to ensure optimal use of available resources. Kubernetes provides greater configuration for management of service deployment to nodes when scaling or when nodes fail. As Etcd is an open-source data store, it can be utilised by the deployed application to store custom application configuration data. Data stored within one Pod instance is distributed to each of the other instances. An Etcd Pod is deployed to each Manager node as replicated units. Kubernetes uses Etcd to manage cluster state. Maintaining state consistency between large numbers of nodes without a third-party store is problematic. This is the reason for a maximum number of Managers. Each Manager node is kept up-to-date with state information so that, should the Leader Manager fail, another Manager can be delegated as Leader and continue the role without significant changes to application stability. Kubernetes can be configured to use a local Ingress load balancer, such as Ingress-Nginx, a simple exposed public port using NodePort, or a third-party load balancer, such as Amazon’s ELB.ĭocker Swarm uses Raft Consensus to manage cluster state. However, while Kubernetes Ingress is standardised, flexible and extensive, the Docker Swarm implementation aims for simplicity and ease of use. Kubernetes Manager nodes are marked with a NoShedule taint to prevent accidental deployment of services to these nodes.īoth Docker Swarm and Kubernetes utilise Ingress networking, which allow the routing of external traffic to internal services. As such, it is considered bad practice to run application services on Kubernetes Manager nodes. Kubernetes Manager nodes run additional containers, known as Pods, that facilitate core Kubernetes functionality.
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Each Manager node can be configured to run application services, though this should be applied with caution. Both Docker Swarm and Kubernetes provide High Availability and both support the inclusion of multiple Manager nodes, required to ensure high availability should the Leader Manager node fail.ĭocker Swarm recommends an odd number of Manager nodes (1 of 3, 3 of 5 etc.) with no more than seven in a given swarm.