Tenma

CAP Theorem CAP Theorem talks about tradoffs of disturbed systems Here C - Consistency (Every read request to the distributed system should return same result irrespective of whichever node we are reading from) A - Availability (The system should respond to any request made to it irrespective of any node is failed or not) P - Partition Tolerance (The system continues to respond/operate even though there is a network breakdown/partition between the nodes) Before Diving into CAP theorem here is some background knowledge you should know Distributed System : Data Stored in multiple servers instead of one(like we do when we apply horizontal scaling) Why distributed systems? > Spread Workload among multiple servers > Can handle more number of requesss > Improves overall performance In distributed system we replicate same data across multiple systems to get the above benifits. Server/s are called a node here. Now let's talk about the CAP Let's say there are there nodes X, Y and Z Consistency says that whenever you read data from X, Y or Z they should return the same data and when you write then it should be propogated to other nodes to maintain consistency Availability says that if B fails due to some hardware issue and go offline then A and C should still be working and should serve the requests Partition Tolerance says if network partition happens on B and it can't communicate with A and C, then node B will still be serving requests even though it is not up to date with the data with other nodes(A and C) since it got a network partition. CAP Theorem: CAP Theorem states that in a distributed system, you can only guarantee two out of these three properties simultaneously. It's impossible to achieve all three You can refer to the image below for clear understand about the statement once Only the combination of CA(Consistency-Availability), AP(Availability-Partition tolerance), CP(Consistency-Partition tolerance) is possible In distributed system there are very high chances of network partition so we should must handle P(partition tolerance). So most of distributed systems choose either AP or CP because they can't afford network partition What to choose between CP and AP CP - if you can't afford inconsistent data then go for CP like banking, payment services where numbers are the most important thing AP - if you can afford in consistent data but can't afford unavailability like social media can have slightly different likes, comments or views for different users but it can't have their apps down.

EC2 and EBS in AWS. EC2- > EC2 is just a machine[computer with cpu, os, ram etc] hosted in cloud by aws which you can use to host your web frontend, backend etc > These EC2 machines are stored in physical locations called availability zone > There are many types of EC2 instances(you need to choose it based upon your application requirements) t and m series are for less workload, c series are computer optimized, etc [You can refer to the image attached below for the categories of EC2 instances] > To launch an instance you need to select instance type + Operating System + Storage Capacity + Security Group(Inbound and outbound) + ssh key pair (to login into the terminal of EC2 instances from your laptop's terminal) + Availability zone(choose nearer zone based on traffic) EBS- > EBS is like a hard drive attached to your EC2 machine. They're used for persistent storage. > EC2 has generally 2 types of storage 1. Instance Storage 2. Elastic Block Store(EBS) 1. Instance Storage - It is a storage that is physically attached to the EC2 instance when you create and start it. - If your EC2 goes power off or gets terminated then all the data stored here in instance storage will be erased since it is a non persistent storage 2. EBS - It is a persistent storage which is not physically attached to the EC2 instance. Even when the EC2 instance is terminated the data will still be stored in EBS - EBS is like an external harddrive - if one EC2(let's say EC2-A) gets terminated which was using EBS, then the same EBS can be used in the new EC2(let's say EC2-B) and it will have the same data as EC2-A - the EC2 instances and EBS should be under the same availability zone Snapshots > yk git commits?, by commits you can track changes in code, revert back to old code when something breaks. Snapshots does the same it captures the current data in the EBS and stores it. > It is used for backups and it stores the disk blocks not files in S3(you don't manage this S3[we'll study about S3 in the upcoming post]) > Snapshots are generally taken daily to take back-up of the valuable data