Elastic Load Balancing automatically distributes incoming application traffic across multiple Amazon EC2 instances for fault tolerance and load distribution. In this session, we go into detail about Elastic Load Balancing's configuration and day-to-day management, as well as its use in conjunction with Auto Scaling. We explain how to make decisions about the service and share best practices and useful tips for success.

1. © 2016, Amazon Web Services, Inc. or its Affiliates. All rights reserved.© 2016, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
David Pessis, Engineering Manager – Elastic Load Balancing
July 13, 2016
Deep Dive on Elastic Load Balancing and
Best Practices

2. Elastic Load Balancing automatically distributes
incoming application traffic across multiple
Amazon EC2 instances.

3. SecureElastic Integrated Cost Effective

4. EC2
Instance

5. Load Balancer used to
route incoming requests
to multiple EC2
instances.
ELB
EC2
Instance
EC2
Instance
EC2
Instance

6. Load balance over classic EC2
instances.
Support for public IP addresses only.
No control over the load balancer
security group.
Load balance over EC2 instances
within a VPC.
Support for both public and private IP
addresses.
Full control over the load balancer
security group.
Tightly integrated into the associated
VPC and subnets.
EC2-Classic EC2-VPC

7. Architecture
Customer VPC
EC2
Instance
EC2
Instance
us-west-1aus-west-1b
Amazon
Route 53
ELB VPC
ELB
ELB

8. HTTP/HTTPSTCP/SSL
Incoming client connection bound to
server connection
No header modification
Proxy Protocol prepends source and
destination IP and ports to request
Round robin algorithm used for
request routing
Connection terminated at the load
balancer and pooled to the server
Headers may be modified
X-Forwarded-For header contains
client IP address
Least outstanding requests algorithm
used for request routing
Sticky session support available

9. Health checks allow for
traffic to be shifted away
from failed instances

10. ELB
EC2
Instance
EC2
Instance
EC2
Instance
Health checks ensure
that request traffic is
shifted away from a
failed instance.
Health Checks

11. Support for TCP and HTTP health checks.
Customize the frequency and failure
thresholds.
Must return a 2xx response.
Consider the depth and accuracy of your
health checks.
Health Checks

12. Idle timeouts allow for connections to be closed by
the load balancer when no longer in use.

13. Length of time that an idle connection should be kept open.
For both client and backend connections.
Defaults to 60 seconds, but can be set between 1 and 3,600
seconds.
Timeouts should decrease as you go
up the stack.
Idle Timeouts

14. 15s
3s
3s
ELB
15s
EC2
Instances
Amazon S3
Amazon RDS
Amazon SWF
3s
9s
Idle Timeouts

15. Using multiple
Availability Zones

16. Multiple Availability Zones
ELB VPC Customer VPC
EC2
InstanceELB
ELB
EC2
Instance
us-west-1aus-west-1b
Amazon
Route 53

17. Multiple Availability Zones
ELB VPC Customer VPC
EC2
InstanceELB
ELB
us-west-1aus-west-1b
Amazon
Route 53

18. Always associate two
or more subnets in
different zones with
the load balancer

19. Using multiple Availability Zones
does bring a few challenges.

20. RequestCount
Time
Traffic Imbalances

21. Imbalanced Instance Capacity
ELB VPC Customer VPC
EC2
InstanceELB
ELB
us-west-1aus-west-1b
Amazon
Route 53
EC2
Instances

22. Cross-Zone Load Balancing
ELB VPC Customer VPC
EC2
InstanceELB
ELB
us-west-1aus-west-1b
Amazon
Route 53
EC2
Instances

23. RequestCount
Time
Traffic Imbalances
Cross-Zone Enabled

24. Load balancer absorbs impact of DNS caching.
Eliminates imbalances in backend instance utilization.
Requests distributed evenly across multiple
Availability Zones.
Check connection limits before enabling.
No additional bandwidth charge for
cross-zone traffic.
Cross-Zone Load Balancing

25. Each load balancer domain may contains multiple records.
Round robin used to balance traffic between Availability Zones.
DNS records will change over time; never
target IP addresses directly.
After being removed from DNS, IP addresses
are drained and quarantined for up to 7 days.
Understanding DNS

26. DNS caching by clients and ISPs can often cause clients to target
a specific IP address or stop resolving at all.
Register a wildcard CNAME or ALIAS within Amazon Route 53.
// Create a wildcard CNAME or ALIAS in Route 53.
*.example.com ALIAS … elb-12345.us-east-1.elb.amazon.com
*.example.com CNAME elb-12345.us-east-1.elb.amazon.com
// prepend random content for each lookup made by the application.
PROMPT> dig +short 25a8ade5-6557-4a54-a60e-8f51f3b195d1.example.com
192.0.2.1
192.0.2.2
DNS Optimization

27. SSL Offloading
Support for both SSL and HTTPs is provided.
Support for latest ciphers and protocols, including
Elliptical Curve Ciphers and Perfect Forward Secrecy.
Ability to fully customize ciphers and protocols to be
used by each load balancer.
SSL Negotiation Suites provided to remove complexity
of selecting ciphers and protocols.

28. SSL Negotiation Policies
Provide selection of ciphers and protocols that adhere to the latest
industry best practices.
Balance security best practices with client’s ability to negotiate a
connection, generated using traffic to Amazon.com.
Released on a regular cadence or when new
vulnerabilities are published.
Default for all new load balancers.

29. POODLE Mitigation
Within 24 hours, 62% of load
balancers migrated to the latest SSL
Negotiation Policy, disabling SSLv3.

30. @awscloud Thank-you #AWS for making it
so easy to prevent #sslv3 #poodleattack Only
took about 3 clicks of my mouse.“
”@granticini

31. 13 CloudWatch metrics provided for each load
balancer.
Provide detailed insight into the health of the load
balancer and application stack.
CloudWatch alarms can be configured to notify or
take action should any metric go outside of the
acceptable range.
All metrics provided at the 1-minute granularity.
Amazon CloudWatch Metrics

32. HealthyHostCount
The count of the number of healthy instances
in each Availability Zone.
Most common cause of unhealthy hosts is
health check exceeding the allocated timeout.
Test by making repeated requests to the
backend instance from another EC2 instance.
View at the zonal dimension.

33. Latency
Measures the elapsed time, in seconds, from when the request leaves the
load balancer until the response is received.
Test by sending requests to the backend instance from another instance.
Using min, average, and max CloudWatch stats,
provide upper and lower bounds for latency.
Debug individual requests using access logs.

34. Surge Queue and Spillovers
Count of the number of requests that could not be sent to backend
instances.
Queue up to 1,024 requests per load balancer
node, after which 503 errors will be returned.
Often caused by not being able to open
connections to the backend instance.
Normally a sign of an under-scaled application.

35. CloudWatch and Auto Scaling
All load balancer metrics can be used for Auto Scaling.
Allows you to scale dynamically, based on the load
balancer's view of the application.
Important to consider all metrics when using
Auto Scaling; may not be aware of resource
contention on another metric.
You may be at peak multiple times a day.

36. Provide detailed information on each
request processed by the load balancer.
Includes request time, client IP address,
latencies, request path, and server
responses.
Delivered to an S3 bucket every 5 or 60
minutes.
Access Logs

37. Access Logs
ELB VPC
ELB
ELB
ELB Amazon S3
Logs indexed by date,
but include the IP
address of the load
balancer node itself.

38. • timestamp
• elb name
• client:port
• backend:port
• request_processing_time
• backend_processing_time
• response_processing_time
• elb_status_code
• backend_state_code
• received_bytes
• sent_bytes
• “request”
2014-02-15T23:39:43.945958Z my-test-loadbalancer
192.168.131.39:2817 10.0.0.0.1 0.000073 0.001048 0.000057 200
200 0 29 "GET http://www.example.com:80/HTTP/1.1"
Access Logs

39. “Everything fails all the time”
Werner Vogels, CTO, Amazon.com

40. Be prepared to do nothing!

41. Mitigation Isolation Restore
Redundancy

42. Mitigation
All load balancers scaled to handle loss
of single Availability Zone.
Route 53 health checks shift traffic away
from the failed Availability Zone.
Completed within 150 seconds.
No other external or control plane
dependencies.

43. Isolation
Other zones must remain unaffected.
Avoid dependencies between zones.
Be careful of work generated as a result
of the event.
Operating at reduced capacity, but
stable.

44. Health checkers and edge locations
perform the same volume of activity
whether endpoints are healthy or
unhealthy.
Constant Work
time
System activity
Time to react
When nothing is failing, volume of API
calls is zero. When failure occurs,
volume of API calls spikes.
time
System activity
Time to react
Work on Failure

45. Restore Redundancy
Restoring the system to full capacity.
Avoid putting additional load on the system
by rushing this step.
Ensure that recovered resources are left in
a consistent state.
Fully recovered when done.

46. Remember to complete
your evaluations!
Remember to complete
your evaluations!

47. Thank You!
Twitter: @davidpessis