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22 February 2024
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Docker Essentials
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Docker is one of those services that you always hear about but may have never used. I never used Docker in college, and I actually never heard of it until I began researching the field of DevOps. Knowing how to use Docker is a quite essential element of becoming a part of a modern development team. My goal of this post is to help the reader gain an understanding of what Docker is
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What is Docker?
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Docker is a set of platform as a service products that use OS-level virtualisation to deliver software in packages called containers. Containers are isolated from one another and bundle their own software, libraries and configuration files; they can communicate with each other through well-defined channels. All containers are run by a single operating-system kernel and are thus more lightweight than virtual machines.
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What is Container?
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Docker Container is a standardised unit which can be created on the fly to deploy a particular application or environment. It could be an Ubuntu container, CentOs container, etc. to full-fill the requirement from an operating system point of view. Also, it could be an application oriented container like CakePHP container or a Tomcat-Ubuntu container etc.
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Docker Concepts
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Docker is a platform for developers and sysadmins to build, share, and run applications with containers. The use of containers to deploy applications is called containerisation. Containers are not new, but their use for easily deploying applications is.
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Containerisation is increasingly popular because containers are:
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+ - Flexible: Even the most complex applications can be containerised.
+ - Lightweight: Containers leverage and share the host kernel, making them much more efficient in terms of system resources than virtual machines.
+ - Portable: You can build locally, deploy to the cloud, and run anywhere.
+ - Loosely coupled: Containers are highly self sufficient and encapsulated, allowing you to replace or upgrade one without disrupting others.
+ - Scalable: You can increase and automatically distribute container replicas across a datacenter.
+ - Secure: Containers apply aggressive constraints and isolations to processes without any configuration required on the part of the user.
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Images and Containers
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Fundamentally, a container is nothing but a running process, with some added encapsulation features applied to it in order to keep it isolated from the host and from other containers. One of the most important aspects of container isolation is that each container interacts with its own, private filesystem; this filesystem is provided by a Docker image. An image includes everything needed to run an application — the code or binary, runtimes, dependencies, and any other filesystem objects required.
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Containers and virtual machines
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A container runs natively on Linux and shares the kernel of the host machine with other containers. It runs a discrete process, taking no more memory than any other executable, making it lightweight.
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By contrast, a virtual machine (VM) runs a full-blown “guest” operating system with virtual access to host resources through a hypervisor. In general, VMs incur a lot of overhead beyond what is being consumed by your application logic.
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lets me summarise the learning till now:
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+ - Virtual Machines are slow and take a lot of time to boot.
+ - Containers are fast and boots quickly as it uses host operating system and shares the relevant libraries.
+ - Containers do not waste or block host resources unlike virtual machines.
+ - Containers have isolated libraries and binaries specific to the application they are running.
+ - Containers are handled by Containerisation engine.
+ - Docker is one of the containerisation platforms which can be used to create and run containers.
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Why do we use docker?
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So we have discussed what Docker is. However, what is the need for the Docker? Well, Docker containers are lightweight and they are super easy to create and deploy.
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Docker provides us with containers. And containerization consists of an entire runtime environment, an application, all its dependencies, libraries, binaries and configuration files needed to run it, bundled into one package. Each application runs separately from the other. Docker solves the dependency problem by keeping the dependency contained inside the containers. It unites developers against dependency of their project.
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Benefits of using Containers over Virtual Machines
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Now let’s discuss what is the benefit of Docker over VMs.
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+ - Unlike VMs( Virtual Machines ) that run on a Guest OS, using a hypervisor, Docker containers run directly on a host server (for Linux), using a Docker engine, making it faster and lightweight.
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+ - Docker containers can be easily integrated compared to VMs.
+ - With a fully virtualized system, you get more isolation. However, it requires more resources. With Docker, you get less isolation. However, as it requires fewer resources, you can run thousands of container on a host.
+ - A VM can take a minimum of one minute to start, while a Docker container usually starts in a fraction of seconds.
+ - Containers are easier to break out of than a Virtual Machine.
+ - Unlike VMs there is no need to preallocate the RAM. Hence docker containers utilize less RAM compared to VMs. So only the amount of RAM that is required is used.
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How does Docker work?
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Since we now understand the benefits of using Docker. Let’s talk above the functioning of Docker. Docker has a docker engine, which is the heart of Docker system. It is a client-server application. It has three main components:
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+ - A server which is a type of long-running process called a daemon process.
+ - A client which is Docker CLI( Command Line Interface), and
+ - A REST API which is used to communicate between the client( Docker CLI ) and the server ( Docker Daemon )
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The Docker daemon receives the command from the client and manages Docker objects, such as images, containers, networks, and volumes. The Docker client and daemon can either run on the same system, or you can connect a Docker client to a remote Docker daemon. They can communicate using a REST API, over UNIX sockets or a network interface.
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In Linux, Docker host runs docker daemon and docker client can be accessed from the terminal.
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In Windows/OS X, there is an additional tool called Docker toolbox. This toolbox installs the docker environment on Win/OS system. This toolbox installs the following: Docker Client, Compose, Kitematic, Machine, and Virtual Box
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Technology used in Docker
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The programming language used in Docker is GO. Docker takes advantage of various features of Linux kernel like namespaces and cgroups.
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namespaces: Docker uses namespaces to provide isolated workspace called containers. When a container is run, docker creates a set of namespaces for it, providing a layer of isolation. Each aspect of a container runs in a separate namespace and its access is limited to that namespace.
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cgroups( control groups ): croups are used to limit and isolate the resource usage( CPU, memory, Disk I/O, network etc ) of a collection of processes. cgroups allow Docker engine to share the available hardware resources to containers and optionally enforce limit and constraints.
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UnionFS( Union file systems ): are file systems that operate by creating layers, making them very lightweight and fast.It is used by Docker engine to provide the building blocks for containers.
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Docker Engine combines the namespaces, cgroups, and UnionFS into a wrapper called a container format. The default container format is libcontainer.
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This is it for now I guess I am a bit tired and will make a second part continuing about docker how to set it up and create our first docker application.
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24 December 2023
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Beginner guide to vim
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+ tl;dr: You want to teach yourself vim (the best text editor known to human kind) in the fastest way possible. This is my way of doing it. You start by learning the minimal to survive, then you integrate all the tricks slowly.
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+ Learn vim and it will be your last text editor. There isn’t any better text editor that I know of. It is hard to learn, but incredible to use.
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+ I suggest you teach yourself Vim in 4 steps:
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+ - Survive
+ - Feel comfortable
+ - Feel Better, Stronger, Faster
+ - Use superpowers of vim
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By the end of this journey, you will become a vim superstar.
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But before we start, just a warning. Learning vim will be painful at first. It will take time. It will be a lot like playing a musical instrument. Don’t expect to be more efficient with vim than with another editor in less than 3 days. In fact it will certainly take 2 weeks instead of 3 days. I was introduced to vim by my ex collegue at Cambium Networks and boy it took me a month to get fluid with this editor.
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1st level - Survive
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+ - Install vim
+ - Launch vim
+ - DO NOTHING! Read
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+ In a standard editor, typing on the keyboard is enough to write something and see it on the screen. Not this time. Vim is in Normal mode. Let’s go to Insert mode. Type the letter i.
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+ You should feel a bit better. You can type letters like in a standard editor. To get back to Normal mode just press the ESC key.
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+ You now know how to switch between Insert and Normal mode. And now, here are the commands that you need in order to survive in Normal mode:
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+ - i → Insert mode. Type ESC to return to Normal mode.
+ - x → Delete the char under the cursor
+ - :wq → Save and Quit (:w save, :q quit)
+ - dd → Delete (and copy) the current line
+ - p → Paste
+ - hjkl → basic cursor move (←↓↑→). Hint: j looks like a down arrow.
+ - :help <command> → Show help about <command>. You can use :help without a <command> to get general help.
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+ Only 5 commands. That is all you need to get started. Once these command start to become natural (maybe after a day or so), you should move on to level 2.
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+ But first, just a little remark about Normal mode. In standard editors, to copy you have to use the Ctrl key (Ctrl-c generally). In fact, when you press Ctrl, it is as if all of your keys change meaning. Using vim in normal mode is a bit like having the editor automatically press the Ctrl key for you.
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+ A last word about notations:
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+ - instead of writing Ctrl-λ, I’ll write <C-λ>.
+ - commands starting with : end with <enter>. For example, when I write :q, I mean :q<enter>.
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2nd Level – Feel comfortable
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+ You know the commands required for survival. It’s time to learn a few more commands. These are my suggestions:
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+ - Insert mode variations:
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+ - a → insert after the cursor
+ - o → insert a new line after the current one
+ - O → insert a new line before the current one
+ - cw → replace from the cursor to the end of the word
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+ - Basic moves
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+ - 0 → go to the first column
+ - ^ → go to the first non-blank character of the line
+ - $ → go to the end of line
+ - g_ → go to the last non-blank character of line
+ - /pattern → search for pattern
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+ - Copy/Paste
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+ - P → paste before, remember p is paste after current position.
+ - yy → copy the current line, easier but equivalent to ddP
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+ - Undo/Redo
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+ - u → undo
+ - <C-r> → redo
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+ - Load/Save/Quit/Change File (Buffer)
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+ - :e <path/to/file> → open
+ - :w → save
+ - :saveas <path/to/file> → save to <path/to/file>
+ - :x, ZZ or :wq → save and quit (:x only save if necessary)
+ - :q! → quit without saving, also: :qa! to quit even if there are modified hidden buffers.
+ - :bn (resp. :bp) → show next (resp. previous) file (buffer)
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Take the time to learn all of these command. Once done, you should be able to do every thing you are able to do in other editors. You may still feel a bit awkward. But follow me to the next level and you’ll see why vim is worth the extra work.
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3rd Level – Better. Stronger. Faster.
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Congratulation for reaching this far! Now we can start with the interesting stuff. At level 3, we’ll only talk about commands which are compatible with the old vi editor.
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Better
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Let’s look at how vim could help you to repeat yourself:
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+ - . → (dot) will repeat the last command,
+ - N<command> → will repeat the command N times.
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+ Some examples, open a file and type:
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+ - 2dd → will delete 2 lines
+ - 3p → will paste the text 3 times
+ - 100idesu [ESC] → will write “desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu desu”
+ - . → Just after the last command will write again the 100 “desu”.
+ - 3. → Will write 3 “desu” (and not 300, how clever).
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Stronger
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Knowing how to move efficiently with vim is very important. Don’t skip this section.
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+ - NG → Go to line N
+ - gg → shortcut for 1G - go to the start of the file
+ - G → Go to last line
+ - Word moves:
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+ - w → go to the start of the following word,
+ - e → go to the end of this word.
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+ By default, words are composed of letters and the underscore character. Let’s call a WORD a group of letter separated by blank characters. If you want to consider WORDS, then just use uppercase characters:
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+ - W → go to the start of the following WORD,
+ - E → go to the end of this WORD.
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Now let’s talk about very efficient moves:
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+ - % :Go to the corresponding ( , { , [ .
+ - * (resp. #) : go to next (resp. previous) occurrence of the word under the cursor
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Believe me, the last three commands are gold.
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Faster
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Remember about the importance of vi moves? Here is the reason. Most commands can be used using the following general format:
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<start position><command><end position>
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For example : 0y$ means
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+ - 0 → go to the beginning of this line
+ - y → yank from here
+ - $ → up to the end of this line
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We also can do things like ye, yank from here to the end of the word. But also y2/foo yank up to the second occurrence of “foo”.
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But what was true for y (yank), is also true for d (delete), v (visual select), gU (uppercase), gu (lowercase), etc…
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4th Level – Vim Superpowers
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With all preceding commands you should be comfortable using vim. But now, here are the killer features. Some of these features were the reason I started to use vim.
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Move on current line: 0 ^ $ g_ f F t T , ;
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+ - 0 → go to column 0
+ - ^ → go to first character on the line
+ - $ → go to the last column
+ - g_ → go to the last character on the line
+ - fa → go to next occurrence of the letter a on the line. , (resp. ;) will find the next (resp. previous) occurrence.
+ - t, → go to just before the character ,.
+ - 3fa → find the 3rd occurrence of a on this line.
+ - F and T → like f and t but backward.
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A useful tip is: dt” → remove everything until the ”.
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Zone selection <action>a<object> or <action>i<object>
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These command can only be used after an operator in visual mode. But they are very powerful. Their main pattern is:
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<action>a<object> or <action>i<object>
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Where action can be any action, for example, d (delete), y (yank), v (select in visual mode). The object can be: w a word, W a WORD (extended word), s a sentence, p a paragraph. But also, natural character such as ", ', ), }, ].
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Suppose the cursor is on the first o of (map (+) ("foo")).
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+ - vi" → will select foo.
+ - va" → will select "foo".
+ - vi) → will select "foo".
+ - va) → will select ("foo").
+ - v2i) → will select map (+) ("foo")
+ - v2a) → will select (map (+) ("foo"))
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Select rectangular blocks: <C-v>.
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Rectangular blocks are very useful for commenting many lines of code. Typically: 0<C-v> <C-d>I-- [ESC]
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+ - ^ → go to the first non-blank character of the line.
+ - <C-v> → Start block selection.
+ - <C-d> → move down (could also be jjj or %, etc…).
+ - I--[ESC] → write -- to comment each line.
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Note: in Windows you might have to use <C-q> instead of <C-v> if your clipboard is not empty.
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Completion: <C-n> and <C-p>.
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In Insert mode, just type the start of a word, then type <C-p>, magic…
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Macros : qa do something q, @a, @@
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qa record your actions in the register a. Then @a will replay the macro saved into the register a as if you typed it. @@ is a shortcut to replay the last executed macro.
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Example
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On a line containing only the number 1, type this:
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+ - qaYp<C-a>q →
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+ - qastart recording.
+ - Ypduplicate this line.
+ - <C-a>increment the number.
+ - qstop recording.
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+ - @a → write 2 under the 1
+ - @@ →write 3 under the 2
+ - Now do 100@@ will create a list of increasing numbers until 103.
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Visual selection: v, V, <C-v>
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We saw an example with <C-v>. There is also v and V. Once the selection has been made, you can:
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+ - J→ join all the lines together.
+ - <(resp. >) → indent to the left (resp. to the right).
+ - = → auto indent
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Add something at the end of all visually selected lines:
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+ - <C-v>
+ - go to desired line (jjj or <C-d> or /pattern or % etc...)
+ - $ go to the end of the line
+ - Awrite text, ESC.
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Splits: :split and vsplit.
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These are the most important commands, but you should look at :help split.
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+ - :split→ create a split (:vsplitcreate a vertical split)
+ - <C-w><dir> : where dir is any ofhjkl) or ←↓↑→ to change the split.
+ - <C-w>_ (resp. <C-w>|) : maximise the size of the split (resp. vertical split)
+ - <C-w>+ (resp. <C-w>-) : Grow (resp. shrink) split
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Conclusion
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That was 90% of the commands I use every day. I suggest that you learn no more than one or two new commands per day. After two to three weeks you’ll start to feel the power of vim in your hands.
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Learning Vim is more a matter of training than plain memorization. Fortunately vim comes with some very good tools and excellent documentation. Run vimtutor until you are familiar with most basic commands. Also, you should read this page carefully: :help usr_02.txt.
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Then, you will learn about !, folds, registers, plugins and many other features. Learn vim like you’d learn piano and all should be fine.
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