DevOps

Question 1

Application Server Setup…

Answer 1

Backup System - required for prod
Recovery Plans - required for prod
Load Balancing
Monitoring
Centralized Logging

Question 2

Server environment for a web application

Answer 2

Consists of the hardware, software, data, operational plans, and personnel that are necessary to keep the application working.

Question 3

Availability

Answer 3

The ability for the application to be usable by its intended users during advertised hours. Availability can be disrupted by any failure that affects a critical component severely enough.

Question 4

Recoverability

Answer 4

The ability to recover an application environment in the event of system failure or data loss. If a critical component fails, and is not recoverable, availability will become non-existent. Improving maintainability, a related concept, reduces the time needed to perform a given recovery process in the event of a failure, and therefore can improve availability in the event of a failure.

Question 5

Performance

Answer 5

The application performs as expected under average or peak load (e.g. it is reasonably responsive). While very important to your users, performance only matters if the application is available

Question 6

Single Point of Failure

Answer 6

Critical components that do not have an automatic failover mechanism.

Question 7

High Availability (HA) setup

Answer 7

An infrastructure without a single point of failure.

That can be achieved by adding redundancy to the entry point, or gateway, to your servers. Achieving a complete HA setup also requires redundancy at every layer of your infrastructure, such as your application and database servers, which is often difficult to implement but can prove to be invaluable for reducing downtime and maintaining a happy user base.

Question 8

Common Server Setups are …

Answer 8

Everything On One Server
Separate Database Server
Load Balancer (Reverse Proxy)
HTTP Accelerator (Caching Reverse Proxy)
Master-Slave Database Replication

Question 9

Active Server

Answer 9

The server that receives user traffic that is forwarded from the Floating IP. Typically, this is a load balancer that forwards the traffic to a backend of web application servers.

Question 10

Passive Server

Answer 10

A standby server that is usually configured identically to the active server. It only will receive traffic during a failover event—i.e. if the active server becomes unavailable, and the Floating IP is remapped to the standby server.

Question 11

Floating IP

Answer 11

The IP address that points to one of the servers, and can be remapped in the event of the failure of the active server.

Floating IP does not automatically provide high availability by itself; a failover mechanism, which automates the process of detecting failures of the active server and reassigning the Floating IP to the passive server, must be devised and implemented for the setup to be considered highly available.

Question 12

Observability is often defined as consisting of three “pillars”:

Answer 12

Logging
Metrics
Tracing

Question 13

The four golden signals (of Google SRE-book fame) consist of:

Answer 13

Latency
Saturation
Traffic
Error

Question 14

Saturation

Answer 14

“Fullness” of a system; it indicates how long something is waiting to be serviced.

Question 15

Latency

Answer 15

Refers to the duration of requests.

Question 16

Traffic

Answer 16

Refers to the amount of demand placed on your system. In a request-based system, this is often measured in HTTP requests per second.

Question 17

Deployment

Answer 17

The step that involves getting the new code onto the servers.

Question 18

Releasing

Answer 18

The step where the new code begins to receive production traffic.

Question 19

Two big disadvantages to scaling vertically…

Answer 19

There are limits defined by the hardware. You cannot scale upwards indefinitely.

It usually requires downtime, something which big corporations cannot afford.

Question 20

Vertical scaling

Answer 20

Adding more resources to the machine.

Horizontal scalability is solving the same problem by throwing more machines at it.

Question 21

Apache Mesos

Answer 21

Is built using the same principles as the Linux kernel, only at a different level of abstraction. The Mesos
kernel runs on every machine and provides applications with API’s for resource management and scheduling across entire datacenter and cloud environments.

It abstracts CPU, memory, storage, and other compute resources away from machines (physical or virtual), enabling fault-tolerant and elastic distributed systems to easily be built and run effectively.

Question 22

Nomad

Answer 22

A single binary that schedules applications and services on Linux, Windows, and Mac. It is an open source scheduler that uses a declarative job file for scheduling virtualized, containerized, and standalone applications.

Question 23

Kubernetes

Answer 23

An open-source system for automating deployment, scaling, and management of containerized applications.

It groups containers that make up an application into logical units for easy management and discovery.

Question 24

Apache Kafka

Answer 24

A distributed, horizontally-scalable, fault-tolerant commit log.

Question 25

Docker Swarm

Answer 25

Provides native clustering functionality for Docker containers, which turns a group of Docker engines into a single, virtual Docker engine.

Question 26

Vagrant

Answer 26

Vagrant is designed primarily for local development environments that use only a handful of virtual machines at most.

A tool for building and managing virtual machine environments in a single workflow. With an easy-to-use workflow and focus on automation, Vagrant lowers development environment setup time, increases production parity, and makes the “works on my machine” excuse a relic of the past.

Question 27

Linux container

Answer 27

A set of processes that are isolated from the rest of the system, running from a distinct image that provides all files necessary to support the processes.

By providing an image that contains all of an application’s dependencies, it is portable and consistent as it moves from development, to testing, and finally to production.

Question 28

Virtualization

Answer 28

Lets many operating systems run simultaneously on a single system (there is a hypervisor).

Virtualization is technology that allows you to create multiple simulated environments or dedicated resources from a single, physical hardware system. Software called a hypervisor connects directly to that hardware and allows you to split 1 system into separate, distinct, and secure environments known as virtual machines (VMs).

Question 29

Control groups (cgroups)

Answer 29

A kernel feature that controls and limits resource usage for a process or groups of processes.

Question 30

systemd

Answer 30

An initialization system that sets up the userspace and manages their processes, is used by cgroups to provide greater control over isolated processes.

Question 31

User namespaces

Answer 31

Allow per-namespace mappings of user and group IDs. In the context of containers, this means that users and groups may have privileges for certain operations inside the container without having those privileges outside the container.

Question 32

Libcontainer

Answer 32

A Docker interface to Linux facilities like Cgroups, namespaces, netlink and netfilter.

Docker engine creates the image,
pass it to containerd,
containerd calls containerd-shim,
containerd-shim uses runC to run the container,
containerd-shim allows the runtime (runC in this case) to exit after it starts the container

Question 33

5 features of cloud computing…

Answer 33

Network, 
pooled resources, 
a user interface, 
provisioning capabilities, 
automatic resource control/allocation

While virtualization creates the network and pooled resources, additional management and operating system software is needed to create a user interface, provision VMs, and control/allocate resources.