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Deployment Architectures

Introduction

DHIS2 application can be deployed using different architectures, including single-server, distributed, hybrid, Docker, and Docker with Kubernetes. The choice of architecture depends on various factors such as simplicity, management complexity, scalability, maintainability, and performance.

The Architecures

  1. single server
    Uses lxd containers, you'll set ansible_connection variable to lxd,
  2. distributed
    dhis2 application stack running on separate servers/Virtual-machines. e.g database server runs on its own VM.
  3. Hybrid A good example here is when you have say postgres running on its own dedicated machine and proxy, dhis2 tomcat instances running from the same server.

Single-server Architecture

In this setup, all components run on the same server. We are using LXD containers to separate application components. The containers are segregated for PostgreSQL, monitoring, instances and proxy, which improves security and resource allocation Its the default choice with ansible tools with ansible_connection=lxd variable set on inventory file.

Features

  • Simplicity
  • Easy to manage
  • Performance

Drawbacks

  • Scalability - scaling individual components is challenging in this kind of a setup.
  • Maintainability
  • Flexibility - less flexible that distributed setup.

Distributed architecture

Here you have components running on their own dedicated servers. For tools to support this architecture, you'll require a deployment server to execute your Ansible scripts. The deployment server must have an SSH connection to the other hosts. You can test the SSH connection using the command: ansible all -m ping -u <ssh_user> -k. Ensure that the ansible_connection parameter is set to SSH, i.e., ansible_connection=ssh, and make sure the IP addresses of the hosts are correctly configured in the inventory file.

To start the installation, follow these steps:

Command Description
sudo ufw limit 22
sudo ufw enable		 Opens ssh port on the host firewall, change 22 to if you are using non default ssh port
cd dhis2-server-tools/deploy/ cd into dhis2-server-tools/deploy/ directory
vim inventory/hosts Edit inventory hosts file and set ansible_connection=ssh
ansible-playbook dhis2.yml -u=your_ssh_user -Kk -K— prompts for sudo password
-k— prompts for ssh password
-u — username for ssh connection

Replace <your_ssh_user> with the appropriate SSH user for the hosts.

ansible_connection=ssh

Strengths

  • scalability - easier to scale individual components independently.
  • fault isolation - Can easily isolate faults since things are decoupled.
  • modularity - is more modular than single server setup.
  • More flexible than single-server architecture.

hybrid

A balanced approach is possible, where the database server is isolated while everything else runs on a single server. This allows you to enjoy the benefits of both configurations.

Docker, lxd and kubernetes

There are other emerging architectures that utilize Docker and Kubernetes as container orchestration layers.