Docker_notes.txt

https://redis.io/download
Redis is an In-memory Data store
I want to install this software 
wget http://download.redis.io/releases/redis-5.0.3.tar.gz
we will get an issue that wget not found
If we want to run redis...using docker 
docker run -it redis
After installing docker:
------------------------
we have to check the following commands:
docker version
docker run hello-world
At the terminal we have executed the command docker run hello-world.That starts up the Docker client or Docker CLI.
Docker CLI will take the commands from you and communicate to the Docker server.
The Docker server will look into the Image cache.If Image cache is empty it will go to dockerhub.The DockerHub is a free public 
repository that you can dowload images and you can run those images.Dockerserver will download the hello-world file and stored into your personal computer
If we run again hello-world program from docker it will not show unable to download image...
Before explaining the container you should have the little background about os
For most of the operating systems there will be something called kernel.
kernel is an intermediate layer acts between process running on your computer and to an hardware.
Two programs running on a computer one is chrome and other is nodejs
chrome in order to work properly has to have python2 and for nodejs has to have python3.In our harddisk we are having an access
to python2.
we can solve this by namespacing..we can make a segments of harddisk for python2 and python3
container is a grouping of resources assigned to it.
How the singlefile(image) will create a container?
An Image is having a snapshot...The snapshot containes the directories and files..
An Image contains chrome and python and also contains specific startup of a command.
Kernel will isolate the harddrive...in container
The file snapshot of the image was taken inside the hard drive..of a container
chrome is a startup command that is isolated from the resources..and placed at running process.

How hello-world world program runs inside the container
we have taken a snapshot from the image and placed in the container... we executed the command hello-world in process

commands:
--------
1) override command
-------------------
docker run busybox echo hi there
hi there it is an extra over ride command..
hi there will be printed out..
docker run busybox echo bye there
docker run busybox echo how are you
docker run busybox ls
echo and ls that exists inside the busybox image.Those are the programs that exist inside the filesystem.
If we run hello-world with ls and echo commands it will give error..
Listing all running containers:
-------------------------------
docker ps -- It will show the running containers...
docker run busybox ping google.com
open another terminal and check now with docker ps-- It will show the status..

docker ps --all
It will show all the containers..

Container lifecycle:
--------------------
docker run = docker create + docker start
docker run is identical of running two other commands.
docker create - creating a container
docker start - starting a container
docker create hello-world -- you will long characters of the string(ID of the container)
docker run -a paste the ID
Then the welcome message appears..
-a -- watch output from the container and print it to the terminal.
Restarting stopped containers:
------------------------------
docker ps --all

docker run busybox hi there
and type docker ps --all
and status will be exited..
we can start the container id:
docker start containerid
docker start -a containerid - we will get the output
To delete all stopped containers:
docker system prune
Retrieving Log Outputs:
-----------------------
docker create busybox echo hi there
docker start containerid
docker logs containerid
you will get the messages...
stopping containers:
--------------------
docker create busybox ping google.com
docker start containerid
docker logs containerid
docker ps
It shows the command google.com
stop command issues a SIGTERM command to a running process
kill command issues a SIGKILL command to a running process

Normal command prompt:
----------------------
redis-server
open another terminal
redis-cli
set mynumber 5
get mynumber

Now in Docker:
--------------
docker run redis
 open another terminal
redis-cli
you will get error messages as could not connect to redis at 127.0.0.1:6379: Connection refused.
Not connected
because redis-cli you are giving outside the container...

Executing commands in running containers:
-----------------------------------------
docker exec -it <containerid> redis-cli

set myvalue 5
get myvalue

-it -- To enter the text.

Getting a command prompt inside the container:
-----------------------------------------------
docker exec -it <containerid> sh
you will see a pound symbol
cd ~/
ls
cd /
echo hi there
export b=5
echo $b

Running:
--------
docker run -it <containerid> sh

Isolation of a container:
-------------------------
1st terminal:
------------
docker run -it busybox sh
2nd terminal:
-------------
docker run -it busybox sh
3rd terminal:
-------------
docker ps

now go to 1st terminal:
-----------------------
touch hithere
ls
Now go to second container and type ls you will not see..

PART3:
-----
Building a custom image:
-----------------------
A Docker file is a plain text file..I have written a couple of lines of configuration placed inside it.
This configuration is going to define how our container behaves.
The Docker client will give the Dockerfile to the Docker server.Dockerserver is going to create a new image..and then starts a container.
mkdir redis-image
cd redis-image
create Dockerfile inside that directory

Building a redis-image:
----------------------
#Use an existing docker image as a Base
FROM alpine

#Download and install a dependency
RUN apk add --update redis

#Tell the image what to do when it starts as a container.
CMD ["redis-server"]

Running:
--------
docker build .
It will create a container id
docker run containerid

Explanation:
-----------
FROM alpine
we want to use the base image as alpine
It is an initial operating system point...to build an image
apk is the package manager that is build in the alpine image.
while we update the image ..Inside the image we will have the copy of redis and we will remove an intermediate container.

Rebuilds with cache:
--------------------
#Use an existing docker image as a Base
FROM alpine

#Download and install a dependency
RUN apk add --update redis
RUN apk add --update gcc

#Tell the image what to do when it starts as a container.
CMD ["redis-server"]

we can use the same image..which is cached in the localmachine

Tagging:
-------
Instead of giving the container id we can give the tag name for an image..
Eg:
---
docker run busybox
docker run redis

docker build -t stephen/redis:latest .
docker run stephen/redis

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PART4:
-----
NODEJS WEBAPP:
-------------
mkdir simpleweb
cd simpleweb
code . --- It will open in the visual editor
create a new file package.json 
npm is not finding the file..
docker build -t stephengrider/simpleweb .

Browser is making a request to 5000 and rediret request to 8080 inside the container.

docker run -p 5000:8080 stephengrider/simpleweb 

open the browser type localhost:5000 --- then output will displayed.

docker exec -it <containerid> sh
/usr/app #

part5:
-----
In the terminal: docker-compose
lot of commands will be displayed
docker-compose.yml
------------------
version: '3'
services:
  redis-server:
    image: 'redis'
  node-app:
    build: .
	ports:
	  - "4001:8081"
stopping:
--------
docker-compose up -d

docker ps

docker-compose down

If he made any changes:
-----------------------
docker-compose up --build
It will rebuild the container
After when we browse in browser
container exited message will be shown in console
docker ps
you can see only one running container

we have to add restart policy for container
version: '3'
services:
  redis-server:
    image: 'redis'
  node-app:
    restart:always
    build: .
	ports:
	  - "4001:8081"