L6a - Cloud as Service

Question 1

On-premise to cloud. List all approaches in order.

Answer 1

1. Traditional on-premise
2. Colocation
3. Hosting
4. Infrastructure as service
5. Platform as service
6. Software as service
7. Serverless

Question 2

What is Iaas?

Answer 2

renting a computer

Question 3

What are the different options for IaaS?

Answer 3

1. renting a VM (actual node is shared)
2. dedicated server (virtualised but not shared)
3. bare metal

Question 4

Who is IaaS good for?

Answer 4

useful to those who need access to computers but can/want to build the rest of the stack themselves

Question 5

List 4 drawbacks of virtualisation (shared setting) ?

Answer 5

1. Performance overheads
2. Performance isolation
3. Shared environments complicate licensing
4. Shared environment may create legal issues

Question 6

Explain PaaS.

Answer 6

You are only responsible for the data and the application.

You get the computers and the middleware, you build
the application.

In Platform as a Service, what is “rented” is not just an instance but the whole software and hardware infrastructure needed to run an application. (including OS).

The user still puts the application together using the services provided but PaaS reduces the amount of code to produce and takes advantage of the cloud features.

Question 7

Why does PaaS make sense? / Why is it possible?

Answer 7

Some apps use the same subset of features.

Question 8

Explain SaaS.

Answer 8

You get the application provided by the cloud, you provide the data to populate it.

e.g. Microsoft Office 365, gmail, Dropbox
e.g. Snowflake for enterprises (data analytics)

Question 9

Explain FaaS.

Answer 9

FaaS (Function as a Service) allows to encapsulate a small application into a function (e.g., a container image) and then the cloud takes over all tasks related to executing it.

Question 10

List 4 properties of FaaS.

Answer 10

1. no reservation of VM or provisioning of instances
2. automatic scalability
3. automatic triggering
4. charged by the millisecond

Question 11

What are the advantages of FaaS?

Answer 11

1. for very short tasks executed rarely, much cheaper (not true for longer tasks, serverless more expensive per hour than VM instances)
2. functions can be started very quickly and automatically (VM instances can take a long time to start and be ready to process data)
3. elasticity is automatic (if more functions are needed, the cloud just spawns more)
4. no need to set up complicated system
5. automatically coupled to events

Question 12

What are the drawbacks of FaaS?

Answer 12

1. stateless
2. short lived
3. no communication across functions

extra: data processing is not good for serverless

Question 13

What is the reasoning behind serverless?

Answer 13

remove the need to deploy a complex infrastructure for every job, automate deployment and execution

Question 14

What does serverless run on?

Answer 14

small footprint VMs/containers

Question 15

How does serverless work, step by step.

Answer 15

1. User provides code for a “function” and selects a size (typically in amount of memory, which maps to a number of virtual CPUs)
2. The function is registered in the system (an image created and stored)
3. The user invokes a function, or it is triggered by an event
4. The serverless platform allocates a micro-VM, loads the image, and starts the function
5. The platform takes care of scaling it up (call more instances of the function) and tear it down when done

Question 16

What are the challenges of serverless for the provider?

Answer 16

1. functions need to stay warm to ensure short start up time (need to reserve containers etc.)
2. scheduling is hard at this level of granularity