Discussion of parent and origin selection at the Fall 2016 ATS summit in Sunnyvale, CA Video: https://www.youtube.com/watch?v=xT-N58i7Cm0

1. Parent & Origin Selection
Fall 2016 ATS summit

2. Parent Selection

3. Parent Selection: features
● Parent selection strategies
○ Round robin load balancing
○ Primary and secondary consistent hash rings
○ Fail over and transaction retry
● Origin servers as parents
○ Fail over and transaction retries.
○ Simple retry search for objects
○ Unavailable server rety
dest_domain=real_example.com parent=”origin1.example.com:80|0.5;origin2.example.com:80|0.5” round_robin=false
parent_is_proxy=false
● Parent health

4. Parent Selection
Edge cache group
parent cache group parent cache group
Edge cache group
Origins (parents)
Failover selection strategyPrimary consistent hash ring
Secondary consistent hash ring

5. Parent Selection: configuration and tuning
● parent.config:
○ Parent lists, rules and selection strategies.
● records.config:
○ Proxy.config.http.parent_routing_enable 0
○ Proxy.config.http.parent_proxy.retry_time 300
○ Proxy.config.http.parent_proxy.fail_threshold 10
○ Proxy.config.http.parent_proxy.total_connect_attempts 4
○ Proxy.config.http.parent_proxy.per_parent_connect_attempts 2
○ Proxy.config.http.parent_proxy.connect_attempts_timeout 30

6. Parent Selection
● TS-4644 - parent selection configuration per remap.
○ map http://example.com http://real_example.com @parent=example_parent.config
○ Lua config file.
● Potential for parent selection plugins.

7. Origin Selection (load balancing)

8. ● LB algorithms
○ RR
○ Consistent hashing
○ Least-connections
● Retry/Redispatch
● Separation of “origin” and “real”
○ Connection limits
○ Queue limit
● “Real” health status
○ Slowstart
○ backup
Origin Selection: Features we want

9. A look at how haproxy does it
● What is different?
○ HAProxy is designed as a Load balancer (not so much as a general purpose proxy)
○ No DNS lookups live-- all done at start
● What is the same?
○ Load balances to N reals
○ Needs to handle flaky downstreams

10. A look at how haproxy does it: a look at the stats

11. What does ATS do today? Origin handling
● proxy.config.http.server_max_connections
● proxy.config.http.connect_attempts_max_retries_dead_server
● proxy.config.http.connect_attempts_max_retries
● proxy.config.http.origin_max_connections
● proxy.config.http.origin_max_connections_queue
● proxy.config.http.origin_min_keep_alive_connections
● proxy.config.http.connect_attempts_rr_retries
● proxy.config.http.connect_attempts_timeout
● proxy.config.http.down_server.cache_time
● proxy.config.http.down_server.abort_threshold

12. Goals / Plans
● Metrics
○ # of reals
○ # of available reals
○ # of connections to VIP
○ # of connections to real
● Handle downstream failures (dns, origins, etc.)
● Per-origin configuration

13. Problems with the separation
● Multiple paths in the HttpSM
● Inconsistencies
○ Selection algorithms
○ Retry logic
○ Usage

14. ● At its core parent selection is a mechanism to control selecting origin
○ Select a real to connect to
○ Potential fall-back to other layers of cache
● At its core origin selection is just a mechanism to pick an IP to connect to
Thoughts on consolidation

15. ● Option 1: Consolidated generator style API for IPs
○ Consolidate HttpSM to only do a single “connect” pass
○ Generator that returns an IP to connect to
○ Failures would send data back to the generator to return another selection
○ Retry logic would be outside (above) this layer
○ Potential to make this accessible as plugin API
● Option 2: Parent selection as an intercept plugin
○ Complete control from the plugin on how fallback and retries work
○ Simplified HttpSM
○ Easily extensible (since it’s not in the core)
Thoughts on consolidation