Single Node Persistence
Problem this snippet solves: A really slick & reliable way to stick to one and only one server in a pool.
Requirement: Direct traffic to only a single node in a pool at a time. Initially, traffic ...
Published Mar 18, 2015
Version 1.0
k20
Nimbostratus
NimbostratusOK people I still don't know how exactly dst addr persistence or iRule will help. Here's what I believe both methods will fail to deliver.
Scenario 1:
T=0, nodes A and B are both online (where T = time), and persistence table is empty T=1, PC1 and PC2 start to connect. 1 of 4 mappings below could happen as persistence entries are created:
- PC1-A and PC2-B
- PC1-B and PC2-A
- PC1-A and PC2-A
- PC1-B and PC2-B
As you can see, we don't want 1 or 2 to happen. Nothing dst addr persistence or iRule could help when persistence entries don't exist yet.
Scenario 2:
T=0, node A online and node B offline, and persistence table is empty. T=1, PC1 and PC2 start to connect. The following mappings will be created in the persistence table:
PC1-A and PC2-A
T=3, node B comes online, PC1, PC2 and PC3 connect. The following mappings could happen:
PC1-A PC2-A PC3-A or PC3-B
As you can see, PC1 and PC2 don't change. However, the new PC3 could go to node A or node B. This will result in some new PC's will go to A or B while the existing PC's will still stick to A due to the existing persistence entries already exist.
Before dst addr persistence or iRule even kicks in, we have to make sure that only ONE node is taking the traffic. How can we accomplish that? Only when this first step is accomplished then dst addr persistence or iRule will help.