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Key DuploCloud concepts

Key concepts for using DuploCloud with Docker and GCP
While deploying Dockerized applications, familiarize yourself with some key concepts and terminologies.

Hosts

These are virtual machines. In GCP deployments, they are also called Worker nodes. By default, apps within a Tenant are pinned to VMs in the same Tenant. DuploCloud has the ability to deploy Hosts in a separate Tenant and apps in other Tenants that leverage these Hosts. This is called Shared Host Model and is not applicable to GCP.

Service

Service is a DuploCloud term. DuploCloud Services are not Kubernetes Services. Services are microservices that are defined by a Name, DockerImage, and a number of replicas in addition to many other optional parameters. Behind the scenes, a DuploCloud Service maps 1:1 either to a Kubernetes deployment set or to a StatefulSet depending on whether the microservice has stateful volumes or not. There are many optional configurations associated with a DuploCloud Service that represent various ways Docker containers can be run. A few of these are:
  • Environment variables
  • Host Network Mode
  • Volume mounts
  • Entrypoint or command overrides
  • Resource caps
  • Health Checks

Allocation Tags

If a service needs to be pinned to run only a specific set of hosts, set an Allocation Tag on the Hosts as well as on the Service. The Allocation Tag is a case-insensitive substring match. For example, an Allocation Tag specified on a service is usually a substring of the tag specified on the host. A Host may be tagged as HighCpu;HighMem and the Service (if tagged highcpu) can be allocated on the Host. However, if the service is tagged highcpu;gpu then it won't be allocated and needs a host that has been tagged highcpu;gpu. If a Service does not have any tag set, it can be placed on any host.
If the Host is tagged with a specific value and you have Services with the same tag, the host is available for any Service which has no tags. If you want the exclusive assignment of a Host to a set of Services, ensure that every Service in the Tenant is tagged with some value.
In the case of Kubernetes deployments, the concept of Allocation Tags maps to labels on nodes, and on node selectors on the deployment set or StatefulSet.
  • Host Networking: By default, Docker containers have their own network addresses. you may want these containers to use the same network interface as the VM. This is called Host Network Mode.
  • Load Balancer: If a service must be accessed by other services, it needs to be exposed using internal and external load balancers.