Key DuploCloud Concepts

Key concepts for using DuploCloud with Docker and Azure

Familiarize yourself with some key concepts and terminologies.

For descriptions of other common DuploCloud concepts, like Infrastructures and Tenants, see the Common Components documentation.

Hosts

These are virtual machines. In AKS deployments, they are also called Worker nodes. By default, apps within a Tenant are pinned to VMs in the same Tenant.

Services

Service is a DuploCloud term. DuploCloud Services are not Kubernetes Services. Services are microservices defined by a Name, Docker image, number of replicas, and 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 it has stateful volumes. Optional configurations represent various ways Docker containers can be run, such as:

• Environment variables

• Host Network Mode

• Volume mounts

• Entrypoint or command overrides

• Resource caps

• Health Checks

If a service needs to be pinned to run only on 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 in case of Docker native deployments and exact match in case of Kubernetes deployments. For example, an Allocation Tag specified on a Docker native Service is usually a substring of the tag specified on the Host. If a Host is tagged HighCpu;HighMem, a Service tagged highcpu can be allocated on it. However, if the Service is tagged highcpu;gpu then it won't be allocated; it would need a Host tagged highcpu;gpu. If a Service does not have any tag set, it can be placed on any Host.

Allocation Tags

Allocation tags allow you to control which Hosts a Service can run on by specifying tags on both the Host and the Service. Services without allocation tags can be scheduled on any Host.

• Docker Services use case-insensitive, substring-based matching. For example, if a Host has the tag HighCpu;HighMem, a Service tagged highcpu or cpu would match and be eligible to run on that Host.

• Kubernetes Deployments use exact, case-sensitive matching based on Kubernetes node labels and node selectors. For example, a Host tagged frontend-prod will only match a Service with the exact same tag: Frontend-Prod or frontend-prod-1 will not match. Kubernetes allocation tags must start and end with an alphanumeric character and may only contain letters, numbers, hyphens (-), or periods (.)

If a Host is tagged and a matching Service exists, the Host may still be used by untagged Services unless all Services in the tenant are tagged. To fully isolate Hosts for a specific purpose, ensure all Services use allocation tags.

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 Balancers

If a service must be accessed by other services, it needs to be exposed using a Load Balancer. Supported Load Balancers include:

• A Network Load Balancer (NLB). An NLB distributes traffic across several servers by using the TCP/IP networking protocol. By combining two or more computers that are running applications into a single virtual cluster, NLB provides reliability and performance for web servers and other mission-critical servers.

• An Application Load Balancer (ALB). An ALB provides outbound connections to cluster nodes inside the AKS virtual network, translating the private IP address to a public IP address as part of its Outbound Pool.