EC2 Amazon Machine Image template from which EC2 instances are launched basic unit of deployment for Amazon EC2 OS + Software launch difference instance types from the same AMI Custom AMIs can be made with customer software, services, configurations and packages Enhanced Networking results in higher bandwidth, higher packet per second (PPS) performance, lower latency, consistency, scalability and lower jitter supportedusing Single Root I/O Virtualization (SR-IOV) only on supported instance types is supported only with an VPC (not EC2 Classic), HVM virtualization type and available by default on Amazon AMI but can be installed on other AMIs as well Placement Group provide low latency, High Performance Computing via10Gbps network is a logical grouping on instances within a Single AZ don’t span availability zones , can span multiple subnets but subnets must be in the same AZ can span across peered VPCs for the same Availability Zones existing instances cannot be moved into an existing placement group for capacity errors, stop and start the instances in the placement group use homogenous instance types which support enhanced networking and launch all the instances at once Elastic Load Balancer & Auto Scaling Elastic Load Balancer Managed load balancing service and scales automatically distributes incoming application traffic across multiple EC2 instances is distributed system that is fault tolerant and actively monitored by AWS scales it as per the demand are engineered to not be a single point of failure need to Pre Warm ELB if the demand is expected to shoot especially during load testing supports routing traffic to instances in multiple AZs in the same region performs Health Checks to route traffic only to the healthy instances support Listeners with HTTP, HTTPS, SSL, TCP protocols has an associated IPv4 and dual stack DNS name can offload the work of encryptionand decryption ( SSL termination ) so that the EC2 instances can focus on their main work supports Cross Zone load balancing to help route traffic evenly across all EC2 instances regardless of the AZs they reside in to help identify the IP address of a client supports Proxy Protocol header for TCP/SSL connections supports X-Forward headers for HTTP/HTTPSconnections supports Stick Sessions (session affinity) to bind a user’s session to a specific application instance, it is not fault tolerant, if an instance is lost the information is lost requires HTTP/HTTPS listener and does not work with TCP requires SSL termination on ELB as it users the headers supports Connection draining to help complete the in-flight requests in case an instance is deregistered For High Availability, it is recommended to attach one subnet per AZ for at least two AZs, even if theinstances arein a single subnet. cannot assign an Elastic IP address to an ELB IPv4 & IPv6 support however VPC does not support IPv6 HTTPS listener does not support Client Side Certificate for SSL termination at backend instances or support for Client Side Certificate useTCP for connections from the client to the ELB, use the SSL protocol for connections from the ELBto theback-end application, and deploy certificates on the back-end instances handlingrequests supports a single SSL certificate , so for multiple SSL certificatemultiple ELBs need to be created Auto Scaling ensures correct number of EC2 instances are always running to handle the load by scalingup or down automatically as demand changes cannot span multiple regions. attempts to distribute instances evenly between the AZs that are enabled for theAuto Scaling group performs checks either using EC2 status checks or can use ELB health checks to determine the health of an instance and terminates the instanceif unhealthy, to launch a new instance can be scaledusing manual scaling, scheduled scaling or demand based scaling cooldown period helps ensure instances are notlaunched or terminated before the previous scalingactivity takes effect toallow the newly launched instances to start handling traffic and reduce load Auto Scaling & ELB can be used for High Availability and Redundancy by spanning Auto Scaling groups across multiple AZs within a region and then setting up ELB to distribute incoming traffic across those AZs With Auto Scaling use ELB health check with the instances to ensure that traffic is routed only to the healthy instances
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