High availability for IP-based Applications

Question 1

how to make an application like this highly available and fault tolerant?

Answer 1

• • Use an EIP;
• • Understand why auto scaling will not work
• • create a standby instances in other availability zones
• • increase instance size to scale.

Question 2

RDS Multi-AZ Failover

Answer 2

provisions and maintains a standby replica in a different AZ
The primary synchronously replicates to the standby instance for redundancy
can reduce downtime in the event of a failure on the primary

Question 3

Replication

Answer 3

• • feature can be turned on from the console or API
• • amazon automatically handles replication
• • the primary instance synchronously replicates to the standby instance for redundancy
• • Replication can cause higher write and commit latency
  • • Using provisioned IOPD is recommended.

Question 4

Other benefits of replication – Patching

Answer 4

patch the standby instance first; failover to the standby instance once the patching is done; patch the primary.

Question 5

Other benefits of replication – Backups

Answer 5

We can eliminate IO locking and minimize latency spikes

create backups from the standby instance.

Question 6

what can trigger a failover?

Answer 6

• • Loss of availability in the primary az
• • loss of network connectivity to the primary instance
• • resource failure with the underlying virtualized resources
• • storage failure on the primary database
• • the db instance’s server type is changed
• • Software/OS patching
• • a manual reboot with failover was initiated.

Question 7

what does not cause a failover?

Answer 7

Responses slow down

corrupted data

Question 8

How do failovers work?

Answer 8

automated by AWS

• • Amazon detects an issue and starts the failover process
• • DNS records are modified to point to the standby instance
• • The application re-establishes any existing DB connections

Question 9

How do we know when a failover happens?

Answer 9

• • Use RDS events to notify via email or SMS
• • Use the API or console to manually check events
• • Use the API or console to check the state of the Multi-AZ deployment.

Question 10

Bastion Hosts

Answer 10

• -“gate” that protects our infrastructure but allows access for updates or other management
• • Used to control remote access
• • for inbound traffic exposed to the internet
• • these should be hardened and secured very carefully and regularly
• • can have an Elastic IP address that never changes and can be whitelisted.
• • We can have standby Bastion Hosts for higher availability