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Ansible Lab #21 - High Availability

Load Balancing：觀念篇

Load balancing 是現代軟體架構者的必備知識。不僅是字面上「負載均衡／平衡」的作用而已，更是 high availability (HA)、zero-downtime deployment 的重要元素。

所以，在許多現代化軟體架構的場合，都可以看到 load balancer 的身影。

這段教學影片中，我介紹 load balancing 所扮演的角色，以及常見的運用場景。

► 影片全長 7 分鐘: http://school.soft-arch.net/courses/vm-for-devops/lectures/964514

實習重點

Topology

  • lb (load balancer): 10.0.0.10
  • app1: 10.0.0.30
  • app2: 10.0.0.31
  • app3: 10.0.0.32
  • db: 10.0.0.20

Identify service dependencies

Vagrant techniques

The Vagrantfile is an ordinary Ruby source file. So, any valid Ruby construct (e.g., variables, conditions, loops) can be used here.

Separation of configuration

Separated by...

  • variables and when conditions;
  • various playbook files;
  • various tags.

Dig more into Ansible's variable system

See Ansible official documents:

See also Vagrant official document:

用到的 module(s)

  • File modules / lineinfile: Ensure a particular line is in a file, or replace an existing line using a back-referenced regular expression.

想接受挑戰嗎？

  • The WordPress application is stateful. You should modify the infrastructure in either way:

    1. In the HAProxy part: use the sticky session mechanism.

    2. In the application server part: use a shared PHP session mechanism.

  • SSL termination.

  • Infrastructure testing.