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M10 caching (cloudfront (webscocket (it is long-held TCP connection. By…

- - - - cloudfront assign DNS to distribution
    - - Means cloudfront send the distribution config to all edge location
      - Not mean sending content of your S3 to edge lcoation
  - - - immediate refresh
        
        Versioning enables you to control which file a request returns even when the user has a version cached either locally or behind a corporate caching proxy.
        
        CloudFront access logs include the names of your files, so versioning makes it easier to analyze the results of file changes.
        
        Versioning provides a way to serve different versions of files to different users.
        
        Versioning simplifies rolling forward and back between file revisions.
        
        Versioning is less expensive. You still have to pay for CloudFront to transfer new versions of your files to edge locations, but you don't have to pay for invalidating files.
        
        Don't have to wait for an object to expire before CloudFront begins to serve a new version of it,
    - - dge location won't get that new version from your origin until both of the following occur:
        
        The old version of the file in the cache expires. For more information, see Managing How Long Content Stays in an Edge Cache (Expiration).
        
        There's a user request for the file at that edge location.
  - - - CloudFront negotiates TLS connections with the highest security ciphers, and authenticates viewers with signed URLs.
      - You can also use our advanced feature Field-Level Encryption to protect most sensitive data throughout your enterprise, so the information can only be viewed by certain components and services
      - in your application stack. CloudFront also integrates with AWS Identity and Access Management (IAM) to control access, with AWS CloudTrail to log access to your configuration, and with Amazon Certificate Manager (ACM) for automated certificate renewals.
- - - - ex: Database join queries slower than simple queries
    - - example facebook personal profile
    - - depend on telerancy level of your appl
    - - cache in browser. ex: html pages, and image
      - rather than query repetitive to server
    - - can be placed in front of client and web servers in order to serve a cached version of the HTTP responses
      - Another name =web application accelerators
      - Protect the server.
      - Make sure no client can talk directly to server
    - - Types of server caching include, but aren’t limited to:
        
        Object caching – Storing database queries in a server-side cache for quick retrieval on subsequent page loads.
        
        CDN caching – A Content Delivery Network (CDN) is a cluster of servers that are geographically located all around the world. They cache content that’s loaded using the server that’s closest to the end user for much faster loading times
  - - - In second or miliseconds
- - - - I am using Memcache currently. Can i migrate to elastic cache
        
        yes,
        
        Is Protocol-compliant with Memcached.
        
        open standard (=same as Redis)
      - Number of nodes required?
        
        For example, if your memory requirement is 13GB, you may want to use two cache.m4.large nodes instead of using one cache.m4.xlarge nod
        
        Need to know total memory required, divide that memory into enough nodes such that your application can survive the loss of one or two nodes.
      - Feature
        
        default maintenance window is 60 minute :DT
      - Mitigating Node failure
        
        spread the cached data over more nodes
        
        as Memcached does not support replication, a node failure will always result in some data loss from the cluster
        
        having more nodes will reduce the proportion of cache data lost
    - - comparison
        
        support Multi-threaded ?
        
        This means that you can handle more operations by scaling up compute capacity.
        
        can make use of multiple processing cores.
        
        Not support Multi AZ
        
        Allocate the nodes in as many availability zones as possible, only the data cached in that AZ is lost, not the data cached in the other
        
        Memcache scale horizontally for write/storage
        
        by adding and removing nodes
        
        Memcache no persistent
        
        Means can't support backup store
        
        Mitigating Node failure
        
        spread the cached data over more nodes
        
        as Memcached does not support replication, a node failure will always result in some data loss from the cluster
        
        having more nodes will reduce the proportion of cache data lost
        
        redis can persistent
        
        Backup and Restore allows users to create snapshots of the Redis clusters
        Snapshots can be used for recovery, restoration, archiving purpose or warm start an ElastiCache for Redis cluster
        
        memcache not support multi-AZ
        
        BUT Nodes can span across multiple AZs within the same region
        
        pub/sub
        
        you send a message to a specific channel not
        
        knowing who, if anyone, receives it. Recipients of the message are those who are subscribed to the channels
      - both also are open source
      - both can support VPC
      - Memcache can support up to 20 nodes; red can support up to 90
      - both support broad set of programming language for their clients: C++, phython, Java script, PHP
      - used case (same like DynamoDB)
        
        significantly lower latency and improve throughput for many
        
        read-heavy application workloads for e.g. social networking, gaming, media sharing and Q&A portals or
        
        compute-intensive workloads such as a recommendation engine
        
        improve application performance by storing critical pieces of data in memory for low-latency access.
        
        be used to cache results of I/O-intensive database queries or the results of computationally-intensive calculations.
      - Advanced data type
        
        In addition to strings, Redis supports lists, sets, sorted sets, hashes, bit arrays, and hyperloglog
        
        Memcache support string
    - - Database protocol
      - feature
        
        support primary DB, read replica, Multi-AZ
      - support adavanced data structure
        
        sorted set and list ,hash
      - can support red replica