Web Applications Flashcards

1
Q

Client tier

A

Client tier is composed by:
* Web clients: HTML + Javascript
* Mobile apps: Android, iOS, etc

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2
Q

Application tier

A

Application tier is composed by:
* REST servers
* Static and dynamic web pages
* Popular application servers
* E.g.: Tomcat, Wildfly, ASP.NET, etc

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3
Q

Data tier

A

Data tier is composed by:
* Filesystems, BLOB stores, key-value stores, SQL databases, etc.
* Other services: caches, message queue, etc.

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4
Q

Why multiple instances of web apps?

A
  1. A single server might not be sufficient to handle all client
    requests;
  2. A single server is a single point of failure: if it fails the
    service becomes unavailable;
  3. A single server may be too far from some clients: latency
    too high.

Insuffient, failure, latency

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5
Q

What is simplicfied by having multiple instances?

A

No internal state in server (state is maintained in the data tier)

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6
Q

App service

A

handles HTTP/REST requests.

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7
Q

database/storage

A

durability

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8
Q

cache

A

improved performance in the servers

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9
Q

CDN

A

reducing load time and save bandwidth

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10
Q

How to avoid downtime in deploying new versions? (Staging)

A

Basic approach:
1. Keep the old version running;
2. Deploy the new version to a staging slot (using Azure
terminology) – instances are created but requests from
clients keep being processed by the old version;
3. (Optionally) warm-up application;
4. Hotswap from the old to the new version, by start
forwarding client requests to the new version.

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