High Availability and Scalability Flashcards
1
Q
Elastic Load Balancer
A
- Clients connect to the listener of the Load Balancer
- LB connects to one or more targets
- Used for HA, Fault Tolerance, and scaling
2
Q
Cross-Zone Load Balancing
A
Load balancing to instances across multiple AZ’s.
- CLB: Disabled by default
- ALB: Enabled by default
- NLB: Disabled by default
3
Q
Types of ASG Scaling Policies
A
- Manual Scaling: manually adjust the desired capacity
- Dynamic Scaling: Action based on a metric (CPU utilisation above 50%)
- Target Tracking Scaling: most simple to setup. I want ASG CPU usage to average 40%.
- Simple/Step Scaling: Use CW alarm to trigger action, such as add two instances when CPU util goes above 90%.
- Scheduled actions: Increae min capacity between 10AM to 2PM on Friday’s.
4
Q
ASG Key Points for Exam
A
- ASG’s are free (only pay for underlying resources)
- Use cooldown periods to avoid rapid scaling
- Use smaller instances to get more granularity
- Use ASG’s with ALB for elasticity - provides abstratction to end users
- ASAG defines WHEN and WHERE you want to launch things. Launch Templates define WHAT is launched (what type of instance, what networking, security groups)
5
Q
Lifecycle hooks
A
Can add actions to EC2 intances, including:
- Pending State: perform given actions before instance is launched
- Terminating: dump data before terminating
