Heroku

Question 1

dependency management tools

Answer 1

Ruby - Bundler

Java - Ivy

Question 2

How do you create an application on Heroku?

Answer 2

heroku create
creates an application on Heroku that is ready for our code
and
attaches a git remote to our local codebase

Question 3

how do you deploy on Heroku?

Answer 3

git push Heroku master

• pushes the code to Heroku
• identifies it
• runs a build process against it making it ready for deployment

Question 4

how can you run the application on Heroku?

Answer 4

Heroku open

Question 5

key segments of the Heroku platform

Answer 5

1-routers - to send user requests (to the applications)
2-dynos - a container where your application runs
3-

Question 6

what is a dyno?

Answer 6

• an isolated, virtualized Unix container where your application runs
• holds our code and configuration, logplex,
• the more running instances of your application are available to take requests
• each dyno is completely isolated from other dynos
• you can add dynos to extend capacity and achieve fault tolerance

Question 7

stateless web apps

Answer 7

-

-recommended because Heroku stops dynos that have slowed or failed and also restarts each dyno every 24 hours

Question 8

environment variables

Answer 8

config vars

Question 9

what is slug compilation?

Answer 9

the process of getting application code into the dyno

Question 10

what is a release in Heroku?

Answer 10

a combination of your application code (or slug) and the configuration around it

• any change to either of these will generate a new release
• this definition of release makes it possible to roll back to previous versions of your code and the configuration surrounding it

Question 11

what is scaling out (horizontal scaling) as opposed to scaling up (vertical scaling)?

Answer 11

• scaling up implies increasing the server capacity

- scaling out implies adding more servers for capacity rather than more capacity to the server

Question 12

Heroku Postgres add-on

Answer 12

provides PostgresQL services to all applications

Question 13

Heroku deployments

Answer 13

• transforms your code into a platform-friendly version that can be scaled up and down instantly and at will
• alters your application to suit the platform, injecting components and configuration
• carried out by Git source control system
• a push into the master branch initiates a deploy

Question 14

What is the difference between speed and throughput?

Answer 14

• speed is how fast your application can take a request and return a single response
• throughput is how many simultaneous requests can be handled at the same time

Question 15

What is CDN?

Answer 15

-Content Delivery Network
-made up of many different machines that are spaced across the globe and are geolocation aware
-

Question 16

N+1 problem

Answer 16

• when we make a call to the database for each of a person’s friends, for example. This means we make N calls for N friends plus 1 call for the original person.
• Instead, call all of the friends at once and keep them in cache?

Question 17

preemptive loading

Answer 17

• using a join to preemptively grab all of the data that we know we will eventually need
• solution for the N+1 problem

Question 18

Postgres Explain function

Answer 18

-a built in function that can be invoked in a query that returns the plan and execution time of the query

Question 19

What are Memcache and Memcachier?

Answer 19

-Two add-ons that both provide access to a volatile store called memcache

Question 20

What do services like New Relic do?

Answer 20

• provides our apps SQL log data and other backend performance characteristics in near real time with easy-to-understand formatted graphs
• many languages and frameworks have instrumentation that allows a client running on production machines to measure and report to these services

Question 21

External performance tools - backend

Answer 21

-

Question 22

External performance tools - frontend-

Answer 22

-

Question 23

latency

Answer 23

-

Question 24

what is fork?

Answer 24

-a way of cloning an application from one location into anothr

Question 25

What database does Heroku use?

Answer 25

PostgreSQL

Question 26

How do you provide for Rails to talk to Postgres?

Answer 26

add the pg gem in the production environment
$ group :production do
    gem 'pg'                    '0.17.1'
    gem 'rails_12factor'  '0.0.2'
end

run bundle install with a special flag to prevent the local installation of any production gems (like these)
$ bundle install –without production
rails_12factor is a gem used by Heroku to serve static assets such as images and style sheets