ELB load balancing algorithm

ELB does round robin load balancing.  However, if you are testing ELB and all of your traffic is going to the same instance, don't be surprised.  This is because Amazon ELB behaves little strange when incoming traffic is originated from Single or  Specific IP ranges, it does not efficiently do round robin and sticks the request to some EC2's only. 

ELB primer : A good place to start

If you are just starting off with ELB or even if you have worked with it for some time, here is a helpful blog post:

http://harish11g.blogspot.com/2012/07/aws-elastic-load-balancing-elb-amazon.html

I like these points in particular: 

Point 4) Amazon ELB is not designed for sudden load spikes /Flash traffic 

Note: Not for traffic that changes ever few seconds or even every few minutes.

Point 8) Amazon ELB cannot do Multi AWS Region Load Balancing

Note: Use Route53

Point 9) Amazon ELB sticks request when traffic is generated from Single IP

Note: I see this a lot in training classes as students are always hitting from same IP address.

Point 12) Amazon ELB can easily support more than 20K+ Concurrent reqs/sec

Note: In most cases, one ELB can support multiple systems.

AWS Direct Connect active active with failover

A common question is: "Can use one direct connect connection as active active but also as failover?"

• Yes, Active/Active(BGPmultipath).Network traffic is load balanced across both connections. If one connection becomes unavailable, all traffic is routed through the other. This is the default configuration. 

Auto Scaling Script

Auto Scaling with VPC 

This example uses the CLI version 1.0.61.2 (API 2011-01-01).  There is now a newer version of the CLI.

Overall notes:

1. Create an image (aka: gold image) that has a health check on it that consists of a simple static HTML page such as a ping.html or an index.html. 

2. The ELB (need an ELB before creating Auto Scaling group) hat has the instances running from your gold image AMI created in step 1. Could potentially (nothing is preventing you from doing) create a auto scale launch configuration (step 6 in process below) with an AMI that is different, with a different instance type as instance type is another parameter of your launch configuration, than the instance that will be part of your auto scaling group.  Both are possible but most will have the same AMI (gold image, so you know you have a health check) and the same instance type.

3. Before you create the ELB you should have instances running of the  gold image to make sure the ELB is working properly.  To provide true HA, make sure to put the instances in two AZs. (for example: us-west-2a, us-west-2b)

4. When creating elb that is using subnets, limitation on ELB is that only one subnet per AZ is allowed.  

5. When creating autoscaling group (as-create-auto-scaling-group)

 need to make sure to specific the VPC subnets and AZs.  The VPC subnets need to be in the AZs specified in the AZ parameter for command.

Steps:

Prework:

1. Identify the VPC : For example, VPC: vpc-9b120cf2

2. Add subnets : In this case, using two public subnets. I had to create the second one (subnet) which was private by default and I had to add an igw to make it public.

3. Subnets -

            A. Subnet: subnet-9f120cf6

            CIDR: 10.0.0.0/24   VPC: vpc-9b120cf2   Availability Zone: us-west-2a

            B. Subnet: subnet-8c130de5

            CIDR: 10.0.5.0/24   VPC: vpc-9b120cf2   Availability Zone: us-west-2b

4. Luanch two instances from AMI that has Apache installed with ping.html (or some other file) as a health check. One instance in subnet A and the other in subnet B. 

5. Create an ELB with the two instances across subnets.  ELB is healthy with two instances running in two AZs in two different public subnets. Limitation on ELB is that one subnet per AZ. 

6. Auto Scaling:

A. as-create-launch-config vpcautoscaling-as-lc --image-id ami-dcd344ec --instance-type t1.micro --key AutoScalingKey

B. as-create-auto-scaling-group vpcautoscaling-as-grp --launch-configuration vpcautoscaling-as-lc  --min-size 4 --max-size 12 --load-balancers VpcautoscalingAutoScalingELB --vpc-zone-identifier subnet-9f120cf6,subnet-8c130de5 --availability-zones us-west-2a,us-west-2b

C. as-describe-auto-scaling-groups --headers

output of command:

INSTANCE  INSTANCE-ID  AVAILABILITY-ZONE  STATE      STATUS   LAUNCH-CONFIG

INSTANCE  i-3af6e708   us-west-2b         InService  Healthy  vpcautoscaling-as-lc

INSTANCE  i-3cf6e70e   us-west-2a         InService  Healthy  vpcautoscaling-as-lc

INSTANCE  i-3ef6e70c   us-west-2a         InService  Healthy  vpcautoscaling-as-lc

INSTANCE  i-38f6e70a   us-west-2b         InService  Healthy  vpcautoscaling-as-lc

D. as-put-scaling-policy vpcautoscaling-scale-out-policy --auto-scaling-group vpcautoscaling-as-grp --adjustment=30 --type PercentChangeInCapacity

ARN: arn:aws:autoscaling:us-west-2:649163059618:scalingPolicy:69270ce4-3350-48f4-9d6f-71bc64225554:autoScalingGroupName/vpcautoscaling-as-grp:policyName/vpcautoscaling-scale-out-policy

E.  as-put-scaling-policy vpcautoscaling-scale-in-policy --auto-scaling-group vpcautoscaling-as-grp --adjustment=1 --type PercentChangeInCapacity

ARM - arn:aws:autoscaling:us-west-2:649163059618:scalingPolicy:d9a6780b-3319-4b00-98f1-e98dcfc68d82:autoScalingGroupName/vpcautoscaling-as-grp:policyName/vpcautoscaling-scale-in-policy

F. mon-put-metric-alarm --alarm-name AddCapacity --metric-name CPUUtilization --namespace "AWS/EC2" --statistic "Average" --evaluation-periods 6 --period 120 --threshold 80 --comparison-operator GreaterThanOrEqualToThreshold --dimensions "AutoScalingGroupName=vpcautoscaling-as-grp"  --alarm-actions arn:aws:autoscaling:us-west-2:649163059618:scalingPolicy:69270ce4-3350-48f4-9d6f-71bc64225554:autoScalingGroupName/vpcautoscaling-as-grp:policyName/vpcautoscaling-scale-out-policy

G. mon-put-metric-alarm --alarm-name RemoveCapacity --metric-name CPUUtilization --namespace "AWS/EC2" --statistic "Average" --evaluation-periods 2 --period 120 --threshold 40 --comparison-operator LessThanOrEqualToThreshold --dimensions "AutoScalingGroupName=vpcautoscaling-as-grp"  --alarm-actions arn:aws:autoscaling:us-west-2:649163059618:scalingPolicy:d9a6780b-3319-4b00-98f1-e98dcfc68d82:autoScalingGroupName/vpcautoscaling-as-grp:policyName/vpcautoscaling-scale-in-policy

H. as-describe-policies --auto-scaling-group vpcautoscaling-as-grp —headers