DevOps Interview Question
1. What is Source Code Management?
It is a process through which we can store and manage any code. Developers
write code, Testers write test cases and DevOps engineers write scripts. This
code, we can store and manage in Source Code Management. Different teams
can store code simultaneously. It saves all changes separately. We can retrieve
this code at any point of time.
2. What are the Advantages of Source Code Management?
. Helps in Achieving teamwork
. Can work on different features simultaneously
. Acts like pipeline b/w offshore & onshore teams
. Track changes (Minute level)
. Different people from the same team, as well as different teams, can store
code simultaneously (Save all changes separately)
3. Available Source Code Management tools in the market?
There are so many Source Code Management tools available in the market.
Those are
. Git
. SVN
. Perforce
. Clear case
Out of all these tools, Git is the most advanced tool in the market where we
are getting so many advantages compared to other Source Code Management
tools.
3. What is Git?
Git is one of the Source Code Management tools where we can store any type
of code. Git is the most advanced tool in the market now. We also call Git is
version control system because every update stored as a new version. At any
point of time, we can get any previous version. We can go back to previous
versions. Every version will have a unique number. That number we call
commit-ID. By using this commit ID, we can track each change i.e. who did
what at what time. For every version, it takes incremental backup instead of
taking the whole backup. That’s why Git occupies less space. Since it is
occupying less space, it is very fast.
4. What are the advantages of Git?
.Speed:-
Git stores every update in the form of versions. For every version, it takes
incremental backup instead of taking the whole backup. Since it is taking less
space, Git is very fast. That incremental backup we call “Snapshot”
.Parallel branching:-
We can create any number of branches as per our requirement. No need to
take prior permission from any one, unlike other Source Code Management
tools. Branching is for parallel development. Git branches allow us to work
simultaneously on multiple features.
.Fully Distributed:-
A backup copy is available in multiple locations in each and everyone’s server
instead of keeping in one central location, unlike other Source Code
Management tools. So even if we lose data from one server, we can recover it
easily. That’s why we call GIT as DVCS (Distributed Version Control System)
5. What are the stages in Git?
There are total of 4 stages in Git
1. Workspace:-
It is the place where we can create files physically and modify. Being a Git user,
we work in this work space.
2. Staging area/Indexing area:-
In this area, Git takes a snapshot for every version. It is a buffer zone between
workspace and local repository. We can’t see this region because it is virtual.
3. Local repository:-
It is the place where Git stores all commit locally. It is a hidden directory so
that no one can delete it accidentally. Every commit will have unique commit
ID.
4. Central repository:-
It is the place where Git stores all commit centrally. It belongs to everyone who
is working in your project. Git Hub is one of the central repositories. Used for
storing the code and sharing the code to others in the team.
6. What is the common branching strategy in Git?
Product is the same, so one repo. But different features.
Each feature has one separate branch
Finally, merge (code) all branches
For Parallel development
Can create any no of branches
Can create one branch on the basis of another branch
Changes are personal to that particular branch
Can put files only in branches (not in repo directly)
The default branch is “Master”
Files created in a workspace will be visible in any of the branch
workspaces until you commit. Once you commit, then that file belongs
to that particular branch.
7. How many types of repositories available in Git?
There are two types of repositories available in Git
Bare Repositories (Central)
These repositories are only for Storing & Sharing the code
All central repositories are bare repositories
Non – Bare Repositories (Local)
In these repositories, we can modify the files
All local /user repositories are Bare Repositories
8. Can you elaborate commit in Git?
Storing file permanently in the local repository we call commit.
For every commit, we get one commit ID
It contains 40 long Alpha-numeric characters
It uses the concept “Check some” (It’s a tool in Linux, generates binary
value equal to the data present in file)
Even if you change one dot, Commit-ID will get changed
Helps in tracking the changes
9. What do you mean by “Snapshot” in Git?
It is a backup copy for each version git stores in a repository.
Snapshot is an incremental backup copy (only backup for new changes)
Snapshot represents some data of particular time so that, we can get
data of particular time by taking that particular snapshot
This snapshot will be taken in Staging area in Git which is present
between Git workspace and Git local repository.
10. What is GitHub?
Git hub is central git repository where we can store code centrally. Git hub
belongs to Microsoft Company. We can create any number of repositories in
Git hub. All public repositories are free and can be accessible by everyone.
Private repositories are not free and can restrict public access for security. We
can copy the repository from one account to other accounts also. This process
we call as “Fork”. In this repository also we can create branches. The default
branch is “Master”
11. What is Git merge?
By default, we get one branch in git local repository called “Master”. We can
create any no of branches for parallel development. We write code for each
feature in each branch so that development happens separately. Finally, we
merge code off all branches in to Master and push to central repository. We
can merge code to any other branch as well. But merging code into master is
standard practice that being followed widely. Sometimes, while merging,
conflict occurs. When same file is in different branches with different code,
when try to merge those branches, conflict occurs. We need to resolve that
conflict manually by rearranging the code.
12. What is Git stash?
We create multiple branches to work simultaneously on multiple features. But
to work on multiple tasks simultaneously in one branch (i.e. on one feature),
we use git stash. Stash is a temporary repository where we can store our
content and bring it back whenever we want to continue with our work with
that stored content. It removes content inside file from working directory and
puts in stashing store and gives clean working directory so that we can start
new work freshly. Later on you can bring back that stashed items to working
directory and can resume your work on that file. Git stash applicable to
modified files. Not new files. Once we finish our work, we can remove all
stashed items form stash repository.
13. What is Git Reset?
Git Reset command is used to remove changes form staging area. This is
bringing back file form staging area to work directory. We use this command
before commit. Often we go with git add accidentally. In this case if we
commit, that file will be committed. Once you commit, commit ID will be
generated and it will be in the knowledge of everyone. So to avoid this one, we
use Git reset.
If you add “–hard” flag to git reset command, in one go, file will be removed
from staging area as well as working directory. We generally go with this one if
we fell that something wrong in the file itself.
15. What is Git Revert?
Git Revert command is used to remove changes from all 3 stages (work
directory, staging area and local repository). We use this command after
commit. Sometimes, we commit accidentally and later on we realize that we
shouldn’t have done that. For this we use Git revert. This operation will
generate new commit ID with some meaningful message to ignore previous
commit where mistake is there. But, here we can’t completely eliminate the
commit where mistake is there. Because Git tracks each and every change.
16. Difference between Git pull and Git clone?
We use these two commands to get changes from central repository. For the
first time if you want whole central repository in your local server, we use git
clone. It brings entire repository to your local server. Next time onwards you
might want only changes instead of whole repository. In this case, we use Git
pull.
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Git clone is to get whole copy of central repository
Git pull is to get only new changes from central repository (Incremental data)
17. What is the difference between Git pull and Fetch?
We use Git pull command to get changes from central repository. In this
operation, internally two commands will get executed. One is Git fetch and
another one is Git merge.
Git fetch means, only bringing changes from central repo to local repo. But
these changes will not be integrated to local repo which is there in your server.
Git merge means, merging changes to your local repository which is there in
your server. Then only you can see these changes.
So Git pull is the combination of Git pull and Git merge.
18. What is the difference between Git merge and rebase?
We often use these commands to merge code in multiple branches. Both are
almost same but few differences. When you run Git merge, one new merge
commit will be generated which is having the history of both development
branches. It preserves the history of both branches. By seeing this merge
commit, everyone will come to know that we merged two branches. If you do
Git rebase, commits in new branch will be applied on top of base branch tip.
There won’t be any merge commit here. It appears that you started working in
one single branch form the beginning. This operation will not preserves the
history of new branch.
19. What is Git Bisect?
Git Bisect we use to pick bad commit out of all good commits. Often
developers do some mistakes. For them it is very difficult to pick that commit
where mistake is there. They go with building all commits one by one to pick
bad commit. But Git bisect made their lives easy. Git bisect divides all commits
equally in to two parts (bisecting equally). Now instead of building each
commit, they go with building both parts. Where ever bad commit is there,
that part build will be failed. We do operation many times till we get bad
commit. So Git bisect allows you to find a bad commit out of good commits.
You don’t have to trace down the bad commit by hand; git-bisect will do that
for you.
20. What is Git squash?
To move multiple commits into its parent so that you end up with one commit.
If you repeat this process multiple times, you can reduce “n” number of
commits to a single one. Finally we will end up with only one parent commit.
We use this operation just to reduce number of commits.
21. What is Git hooks?
We often call this as web hooks as well. By default we get some configuration
files when you install git. These files we use to set some permissions and
notification purpose. We have different types of hooks (pre commit hooks &
post commit hooks)
Pre-commit hooks:- Sometimes you would want every member in your team to
follow certain pattern while giving commit message. Then only it should allow
them to commit. These type of restrictions we call pre-commit hooks.
Post-commit hooks:- Sometimes, being a manager you would want an email
notification regarding every commit occurs in a central repository. This kind of
things we call post-commit hooks.
In simple terms, hooks are nothing but scripts to put some restrictions.
22. What is Git cherry-pick?
When you go with git merge, all commits which are there in new development
branch will be merged into current branch where you are. But sometimes,
requirement will be in such that you would want to get only one commit form
development branch instead of merging all commits. In this case we go with git
cherry-pick. Git cherry-pick will pick only one commit whatever you select and
merges with commits which are there in your current branch. So picking
particular commit and merging into your current branch we call git cherry-pick.
23. What is the difference between Git and SVN?
SVN:-
It is centralized version control system (CVCS) where back up copy will be
placed in only one central repository.
There is no branching strategy in SVN. You can’t create branches. So no parallel
development.
There is no local repository. So can’t save anything locally. Every time after
writing code you need to push that code to central repository immediately to
save changes.
Git:-
It is a Distributed version control system where back up copy is available in
everyone’s machine’s local repository as well as a central repository.
We can create any no of branches as we want. So we can go in parallel
development simultaneously.
Every Git repository will have its own local repository. So we can save changes
locally. At the end of our work finally, we can push code to a central repository.
24. What is the commit message in Git?
Every time we commit, while committing, we have to give commit message
just to identify each commit. We can’t remember to commit numbers because
they contain 40 long alphanumeric characters. So, to remember commits
easily, we give commit message. The format of commit message differs from
company to company and individual to individual.
We have one more way to identify commits. That is giving “Tags”. Tag is a kind
of meaningful name to a particular commit. Instead of referring to commit ID,
we can refer to tags. Internally tag will refer to respective commit ID.
These are the ways to get a particular commit easily.
26. What is Configuration Management?
It is a method through we automate admin tasks. Each and every minute
details of a system, we call configuration details. If we do any change here
means we are changing the configuration of a machine. That means we are
managing the configuration of the machine. System administrators used to
manage the configuration of machine through manually. DevOps engineers are
managing this configuration through automated way by using some tools
which are available in the market. That’s why we call these tools as
configuration management tools.
27. What is IAC?
IAC means Infrastructure As Code. It is the process through which we
automate all admin tasks. Here we write code in Ruby script in chef. When you
apply this code, automatically code will be converted into Infrastructure. So
here we are getting so many advantages in writing the code. Those are
1. Code is Testable (Testing code is easy compare to Infrastructure)
2. Code is Repeatable (Can re-use the same code again and again)
3. Code is Versionable (Can store in versions so that can get any previous
versions at any time)
28. What do you mean by IT Infrastructure??
IT Infrastructure is a composite of the following things
Software
Network
People
Process
29. What are the problems that system admins used to face earlier when there
were no configuration management tools?
1. Managing users & Groups is big hectic thing (create users and groups,
delete, edit……)
2. Dealing with packages (Installing, Upgrading & Uninstalling)
3. Taking backups on regular basis manually
4. Deploying all kinds of applications in servers
5. Configure services (Starting, stopping and restarting services)
These are some problems that system administrators used to face earlier in
their manual process of managing configuration of any machine.
30. Why should we go with Configuration Management Tool?
1. By using the Configuration Management Tool, we can automate almost each
and every admin task.
2. We can increase uptime so that can provide maximum user satisfaction.
3. Improve the performance of systems.
4. Ensure compliance
5. Prevent errors as tools won’t do any errors
6. Reduce cost (Buy tool once and use 24/7)
31. How this Configuration Management Tool works?
Whatever system admins (Linux/windows) used to do manually, now we are
automating all those tasks by using any Configuration Management Tool. We
can use this tool whether your servers are in on-premises or in the cloud. It
turns your code into infrastructure. So your code is versionable, repeatable
and testable. You only need to tell what the desired configuration should be,
not how to achieve it. Through automation, we get our desired state of server.
This is unique feature of Configuration Management Tool.
32. What is the architecture of Chef?
Chef is an administration tool. In this we have total 3 stages.
1. Chef Workstation (It is the place where we write code)
2. Chef Server (It is the place where we store code)
3. Chef Node (It is the place where we apply code)
We need to establish communication among workstation, server and nodes.
You can have any no of nodes. There is no limit. Chef can manage any no of
nodes effectively.
33. Components of Chef?
Chef Workstation: Where you write the code
Chef Server: Where you upload the code
Chef Node: Where you apply the code
Knife: Tool to establish communication among workstation, server & node.
Chef-client: Tool runs on every chef node to pull code from chef server
Ohai: Maintains current state information of chef node (System Discovery
Tool)
Idempotency: Tracking the state of system resources to ensure that the
changes should not re-apply repeatedly.
Chef Supermarket: Where you get custom code
34. How does Chef Works?
We need to install chef package in workstation, server and nodes. We create
cookbook in workstation. Inside cookbook, there will be a default recipe where
you write code in ruby script. You can create any no of recipes. There is no
limit. After writing code in recipe, we upload whole cookbook to chef server.
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Chef server acts as central hub storing code. Then, we need to add this
cookbook’s recipe to nodes run-list. Chef-client tool will be there in each and
every chef node. It runs frequently. Chef-client comes to chef server and take
that code and applies that code in node. This is how code will be converted
into infrastructure.
35. What is Idempotency?
It is unique feature in all configuration management tools. It ensures that
changes should not re-apply repeatedly. Once chef-client converted code into
Infrastructure, then even chef-client runs again, it will not take any action. It
won’t do the same task again and again. If any new changes are there in that
code, then only chef-client is going to take action. So it doesn’t make any
difference ever if you run chef-client any no of times. So tracking the system
details to not to reapply changes again and again, we call Idempotency.
36. What is Ohai and how does it works??
Ohai we call “System Discovery Tool”. It stores system information. It captures
each and every minute details of system and updates it then and there if any
new changes are there. Whenever chef-client converts code in infrastructure in
node, immediately Ohai store will be updated. Next time onwards, before
chef-client runs, it verifies in Ohai store to know about current state of
information. So chef-client will come to know the current state of server. Then
chef-client acts accordingly. If new changes are there, then only it will take
action. If there are no new changes, then it won’t take any action. Ohai tool
helps in achieving this.
37. How many types of chef server?
Total there are 3 ways through which we can manage chef server.
1. Directly we can take chef server from Chef Company itself. In this case,
everything will be managed by Chef Company. You will get support from chef.
This type of server we call Managed/Hosted chef. This is completely Graphical
User Interface (GUI). It’s not free. We need to pay to Chef Company after
exceeding free tier limit.
2. We can launch one server and we need to install chef server package. It is
completely free package. It’s GUI.
3. We can launch one server and we need to install chef server package. It is
completely free package. It’s CLI (Command Line Interface).
38. What is there inside cookbook??
Below mentioned files and folders will be there inside cookbook when you first
create it
Chefignore: like .gitignore (to ignore files and folders)
Kitchen.yml: for testing of cookbook
Metadata.rb: name, author, version…. etc of cookbook
Readme.md: information about usage of cookbook
Recipe: It is a file where you write code
Spec: for unit test
Test: for integration test
39. What is Attributes concept in chef?
Sometimes we might need to deploy web applications to in nodes and for that
we need to know some host specific details of each server like IP Address, Host
name ….. etc. Because we need to mention that in configuration files of each
server. These files we call as Configuration files. This information will be vary
from system to system. These host specific details that we mention in
Configuration files,we call “Attributes”. Chef-client tool gathers these
Attributes from Ohai store and puts in configuration files. Instead of hard
coding these attributes, we mention as variables so that every time, file will be
updated with latest details of their respective nodes.
40. What is Run-list in Chef?
This is an ordered list of recipes that we are going to apply to nodes. We
mention all recipes in cookbook and then we upload that cookbook to chef
server. Then, we attach all recipes to nodes run-list in sequence order. When
chef-client runs, it applies all recipes to nodes in the same order whatever the
order you mention in run-list. Because sometimes order is important especially
when we deal with dependent recipes.
41. What is bootstrap?
It is the process of adding chef node to chef server or we can call, bringing any
machine into chef environment. In this bootstrapping process total three
action will be performed automatically.
1. Node gets connected to chef server.
2. Chef server will install chef package in chef node.
3. Cookbooks will be applied to chef node.
It is only one time effort. As and when we purchase any new machine in
company, immediately we add that server to chef server. At a time, we can
bootstrap one machine. We can’t bootstrap multiple machines at a time.
42. What is the workflow of Chef?
We connect chef workstation, chef server and chef node with each other. After
that, we create cookbook in chef workstation and inside that cookbook, we
write code in recipe w.r.t. the infrastructure to be created. Then we upload
entire cookbook to chef server and attach that cookbook’s recipe to nodes run-
list. Now we automate chef-client which will be there in all chef nodes. Chef-
client runs frequently towards chef server for new code. So chef-client will get
that code from server and finally applies to chef node. This is how, code is
converted into infrastructure. If no changes are there in code, even if chef-
client runs any no of time, it won’t take any action until it finds some changes
in code. This is what we call Idempotency.
43. How does we connect Chef Workstation to Chef Server?
First we download started kit from chef server. This will be downloaded in the
form of zip file. If we extract this zip file, we will get chef-repo folder. This chef-
repo folder we need to place in chef workstation. Inside chef-repo folder, we
can see total three folders. They are .chef, cookbooks and roles. Out of these
three, .chef folder is responsible to establish communication between chef
server and chef workstation. Because, inside .chef folder, we can see two files.
They are knife.rb and organization.pem. Inside kinfe.rb, there will be the url
(address) of chef server. Because of this url, communication will be established
between chef server and chef workstation. This is how we connect Chef
Workstation to Chef Server.
44. How does the chef-client runs automatically?
By default, chef-client runs manually. So we need to automate this manually.
For this, we use “cron tool” which is the default tool in all Linux machines use
to schedule tasks to be executed automatically at frequent intervals. So in this
“crontab” file, we give chef-client command and we need to set the timing as
per our requirement. Then onwards chef-client runs automatically after every
frequent intervals. It is only one time effort. When we purchase any new
server in company, along with bootstrap, we automate chef-client then and
there.
45. What is chef supermarket?
Chef supermarket is the place where we get custom cookbooks. Every time we
need not to create cookbooks and need not to write code from scratch. We
can go with custom cookbooks which are available in chef supermarket being
provided by chef organization and community. We can download these
cookbooks and modify as per our needs. We get almost each and every
cookbook from chef supermarket. They are safe to use.
46. What is wrapper cookbook?
Either we can download those chef supermarket cookbooks or without
downloading, we can call these supermarket cookbooks during run time so
that every time we get updates automatically for that cookbook if any new
updates are there. Here, we use our own cookbook to call chef supermarket
cookbook. This process of calling cookbook by using another cookbook, we call
wrapper cookbook. Especially, we use this concept to automate chef-client.
47. What is “roles” in chef?
Roles are nothing but a Custom run-list. We create role & upload to chef server
& assign them to nodes. If we have so many nodes, need to add cookbook to
run-list of all those nodes, it is very difficult to attach to all nodes run-list. So,
we create role & attach that role to all those nodes once. Next time onwards,
add cookbook to that role. Automatically, that cookbook will be attached to all
those nodes. So role is one time effort. Instead of adding cookbooks to each &
every node’s run-list always, just create a role & attach that role to nodes.
When we add cookbook to that role, it will be automatically applied to all
nodes those assigned with that role.
48. What is include_recipe in chef?
By default, we can call one recipe at a time in one cookbook. But if you want to
call multiple recipes from same cookbook, we use include_recipe concept.
Here, we take default recipe and we mention all recipes to be called in this
default recipe in an order. If we call default recipe, automatically default recipe
will call all other recipes which are there inside default recipe. By using one
recipe, we can call any no of recipes. This process of calling one recipe by using
other recipe, we call as include_recipe. Here condition is we can call recipes
from same cookbook, but not from different cookbooks.
49. How to deploy a web server by using chef?
package ‘httpd’ do
action :install
end
file ‘/var/www/html/index.html’ do
content ‘Hello Dear Students!!’
action :create
end
service ‘httpd’ do
action [ :enable, :start ]
end
50. How to write ruby code to create file, directory?
file ‘/myfile’ do
content ‘This is my second file’
action :create
owner ‘root’
group ‘root’
end
directory ‘/mydir’ do
action :create
owner ‘root’
group ‘root’
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end
51. How to write ruby code to create user, group and install package?
user ‘user1’ do
action: create
end
group ‘group1’ do
action :create
members ‘user1’
append true
end
package ‘httpd’ do
action: install
end
52. What is container?
The container is like a virtual machine in which we can deploy any type of
applications, soft wares and libraries. It’s a light weight virtual machine which
uses OS in the form of image, which is having less in size compare to traditional
VMware and oracle virtual box OS images. Container word has been taken
from shipping containers. It has everything to run an application.
53. What is virtualization?
Logically dividing big machine into multiple virtual machines so that each
virtual machine acts as new server and we can deploy any kind of applications
in it. For this first we install any virtualization software on top of base OS. This
virtualization software will divide base machine resources in to logical
components. In a simple terms, logically dividing one machine into multiple
machines we call virtualization.
54. What is Docker?
Docker is a tool by using which, we create containers in less time. Docker uses
light weight OS in the form of docker images that we will get from docker hub.
Docker is open source now. It became so popular because of its unique
virtualization concept called “Containerization” which is not there in other
tools. We can use docker in both windows and Linux machines.
55. What do you mean by docker image?
Docker image is light weight OS provided by docker company. We can get any
type of docker image form docker hub. We use these docker images to create
docker containers. This docker images may contain only OS or OS + other soft
wares as well. Each software in docker image, will be stored in the form of
layer. Advantage of using docker images is, we can replicate the same
environment any no of times.
56. What are the ways through which we can create docker images?
There are three ways through which we can create docker images.
1. We can take any type of docker image directly from docker hub being
provided by docker company and docker community.
2. We can create our own docker images form our own docker containers. I.e.
first we create container form base docker image taken form docker hub and
then by going inside container, we install all required soft wares and then
create docker image from our own docker container.
3. We can create docker image form docker file. It is the most preferred way of
creating docker images.
57. What is docker file and why do we use it?
It is a just normal text file with instructions in it to build docker image. It is the
automated way of creating docker images. Once you build docker image,
automatically docker file will be created. In this file, we mention required OS
image and all required soft wares in the form of instructions. Once we build
docker file, back end, docker container will be created and then docker image
will be crated from that container and that container will be destroyed
automatically.
58. Difference between docker and VM Ware?
VM Ware uses complete OS which contains GBs in size. But docker image size
is MBs only. So it takes less size. That’s why it takes less base machine
resources. This docker image is compressed version of OS. The second
advantage of docker is, there is no pre-allocation of RAM. During run time, it
takes RAM as pre requirement from base machine and one’s job is done, it
release RAM. But in VM Ware, pre-allocation of RAM is there and it blocked
whether it uses or not. So need more RAM for base machine if you want to use
VM Ware unlike Docker.
59. What is OS-Lever Virtualization?
It is the unique feature of Docker which is not available in other virtualization
soft wares. Docker takes most of UNIX features form host machine OS and it
only takes extra layers of required OS in the form of docker image. So docker
image contains only extra layers of required OS. For core UNIX kernel, it
depends upon host OS, why because UNIX kernel is same in any of the UNIX
and Linux flavors. In a simple terms, docker takes host OS virtually. That’s why
we call this concept as OS-Lever Virtualization.
60. What is Layered file system/Union file system?
Inside docker container, wheat ever we do, that forms as a new layer. For
instance, creating files, directories, installing packages etc. This is what we call
as layered file system. Each layer takes less space. We can create docker image
form this container. In that docker image also we get all these layers and forms
unity. That’s why we also call Union File System. If we create container out of
docker image, you can able to see all those files, directories and packages. This
is what replication of same environment.
61. What are the benefits of Docker?
Containerization (OS level virtualization) (No need guest OS)
No pre-allocation of RAM
Can replicate same environment
Less cost
Less weight (MB’s in size)
Fast to fire up
Can run on physical/virtual/cloud
Can re-use (same image)
Can create containers in less time
62. List of Docker components?
Docker image: – Contains OS (very small) (almost negligible) + soft wares
Docker Container: – Container like a machine which is created from Docker
image.
Docker file: – Describes steps to create a docker image.
Docker hub/registry: – Stores all docker images publicly.
Docker daemon: – Docker service runs at back end
Above five components we call as Docker components
63. What is Docker workflow?
First we create Docker file by mentioning instructions to build docker image.
Form this Docker image, we are going to create Docker container. This Docker
image we can push to docker hub as well. This image can be pulled by others
to create docker containers. We can create docker images from docker
containers. Like this we can create Docker images form either docker file or
docker containers. We can create docker containers from docker images. This
is the work flow of docker.
64. Sample Docker file instructions?
FROM ubuntu
WORKDIR /tmp
RUN echo “Hello” > /tmp/testfile
ENV myname user1
COPY testfile1 /tmp
ADD test.tar.gz /tmp
65. What is the importance of volumes in Docker?
Volume is a directory inside your container
First declare directory as a volume and then share volume
Even if we stop container, still we can access volume
Volume will be created in one container
You can share one volume across any no of containers
Volume will not be included when you update an image
Map volumes in two ways
Share host – container
Share container – container
66. What do you mean by port mapping in Docker?
Suppose if you want to make any container as web server by installing web
package in it, you need to provide containers IP address to public in order to
access website which is running inside docker container. But Docker containers
don’t have an IP address. So, to address this issue, we have a concept called
Docker port mapping. We map host port with container port and customers
use public IP of host machine. Then their request will be routed from host port
to container’s port and will be loaded web page which is running inside docker
container. This is how we can access website which is running inside container
through port mapping.
67. What is Registry server in Docker?
Registry server is our own docker hub created to store private docker images
instead of storing in public Docker hub. Registry server is one of the docker
containers. We create this Registry server from “registry” image, especially
provided by docker to create private docker hub. We can store any no of
private docker images in this Registry server. We can give access to others, so
that, they also can store their docker images whomever you provide access.
Whenever we want, we can pull these images and can create containers out of
these images.
68. Important docker commands?
1. Docker ps (to see list of running containers)
2. Docker ps -a (to see list of all containers)
3. Docker images (to see list of all images)
4. Docker run (to create docker container)
4. Docker attach (to go inside container)
6. Docker stop (to stop container)
7. Docker start (to start container)
8. Docker commit (to create image out of docker file)
9. Docker rm (to delete container)
10. Docker rmi (to delete image)
69. What is Ansible?