> For the complete documentation index, see [llms.txt](https://amanalok.gitbook.io/mlops/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://amanalok.gitbook.io/mlops/docker/introduction-to-docker.md). # Introduction to Docker After installing Docker, one can check its version by the following command: ```bash docker version ``` The output of the above command would be somethign like below: ```bash Client: Cloud integration: v1.0.25 Version: 20.10.16 API version: 1.41 Go version: go1.17.10 Git commit: aa7e414 Built: Thu May 12 09:20:34 2022 OS/Arch: darwin/arm64 Context: default Experimental: true Server: Docker Desktop 4.9.1 (81317) Engine: Version: 20.10.16 API version: 1.41 (minimum version 1.12) Go version: go1.17.10 Git commit: f756502 Built: Thu May 12 09:14:19 2022 OS/Arch: linux/arm64 Experimental: false containerd: Version: 1.6.4 GitCommit: 212e8b6fa2f44b9c21b2798135fc6fb7c53efc16 runc: Version: 1.1.1 GitCommit: v1.1.1-0-g52de29d docker-init: Version: 0.19.0 GitCommit: de40ad0 ``` ## Hello World We would execute the following command now: ```bash docker run hello-world Hello from Docker! ``` For the above command, docker takes the following steps: * The Docker client contacted the Docker daemon. * The Docker daemon pulled the "hello-world" image from the Docker Hub. (arm64v8) * The Docker daemon created a new container from that image which runs the executable that produces the output you are currently reading. * The Docker daemon streamed that output to the Docker client, which sent it to your terminal. ## Docker CLI ### docker run The first command we would look in details is the `docker run` command. The below figure provides details about this command: ![](/files/qHqCZw9xT4XVZ4BFtE5J) The `docker run` command is used for creating and running a container from an image. ### Overriding Default Commands To override the default startup command, the following figure shows how to do it: ![](/files/BWbaDFLBwyTiwequJQT2) For example, following command uses a override command with `docker run`: ```bash docker run busybox echo hi there ``` Output would be: ```bash hi there ``` Another example is listing out the files and directories within a container: ```bash docker run busybox ls ``` Output of the above command would be: ```bash bin dev etc home proc root sys tmp usr var ``` Now, let's try the `echo` and `ls` override commands with the `hello-world` image with `docker run`. ```bash docker run hello-world ls docker: Error response from daemon: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: exec: "ls": executable file not found in $PATH: unknown. ERRO[0000] error waiting for container: context canceled docker run hello-world echo hi there docker: Error response from daemon: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: exec: "echo": executable file not found in $PATH: unknown. ERRO[0000] error waiting for container: context canceled ``` As we can observe, we get an error for both the commands. This is because inside the `hello-world` image file-system, the `ls` and `echo` programs do not exist. The only thing that exists inside the `hello-world` image snaphot file-system is a single program. All this program does is print out the singular message: `Hello from Docker!`. The same commands work with the `busybox` image because these programs exist inside the `busybox` file-system image. ### Listing Running Containers Next, we will look at a command to list all currently running containers on a local machine. ![](/files/kzEOGD1mPzTUKtnBmVjf) First of all we will run a container for a meaningful amount of time, like below: ```bash docker run busybox ping google.com PING google.com (172.217.161.14): 56 data bytes 64 bytes from 172.217.161.14: seq=0 ttl=37 time=11.497 ms 64 bytes from 172.217.161.14: seq=1 ttl=37 time=12.000 ms 64 bytes from 172.217.161.14: seq=2 ttl=37 time=18.183 ms 64 bytes from 172.217.161.14: seq=3 ttl=37 time=13.093 ms 64 bytes from 172.217.161.14: seq=4 ttl=37 time=11.236 ms ``` Next, we would list the running containers: ```bash docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES b60202284ace busybox "ping google.com" 2 minutes ago Up 2 minutes exciting_tharp ``` As can be observed from the output of the command, it prints out a bunch of information about the running container. We can modify the `docker ps` command to list all containers created on a local machine like the following: ```bash docker ps --all ``` Executing the above command will give the output something like below: ```bash CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES b60202284ace busybox "ping google.com" 3 hours ago Exited (0) 3 hours ago exciting_tharp 298176ed2948 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago zen_johnson 38f01afc355f hello-world "echo hi there" 3 hours ago Created distracted_austin b25255cc9ef7 hello-world "ls" 3 hours ago Created awesome_swirles b09147ec3aae busybox "ls" 4 hours ago Exited (0) 4 hours ago youthful_wu ab8b6c0bf713 busybox "echo hi there" 4 hours ago Exited (0) 4 hours ago wonderful_archimedes 9435b6d0c6f7 hello-world "/hello" 5 hours ago Exited (0) 5 hours ago xenodochial_kepler ``` ### Container Lifecycle The `docker run` command is actually equivalent to running 2 seperate commands as detailed below: ![](/files/wMRbGJKcfwBBKYyLcApv) The `docker create` command creates a container while the `docker start` command starts a container: ![](/files/4bwHqjUbRhiB9LxlJj28) For example, the below command creates a new container using the `hello-world` image: ```bash docker create hello-world 43b0148310bad8560734d780be5b7f7aac788b646a046efaa93e50d4558395d9 ``` As can be observed, the `docker create` command outputs the id of the container that was created. Next, we can execute the `hello world` command inside of this container using `docker start`, like below: ```bash docker start -a 43b0148310bad8560734d780be5b7f7aac788b646a046efaa93e50d4558395d9 ``` Like running the `docker run` command, the above command will output the following: ```bash Hello from Docker! ``` Running `docker start` without the `-a` arguement does the following: ```bash docker start 43b0148310bad8560734d780be5b7f7aac788b646a046efaa93e50d4558395d9 43b0148310bad8560734d780be5b7f7aac788b646a046efaa93e50d4558395d9 ``` As can be observed above, without the `-a` argement, the command returns back the id of the container. The `-a` arguement will make docker actually watch for output from the container and print it out on the terminal. ### Restarting Stopped Containers An exited container can be started back again. For example, first we list all the containers created on a machine like below: ```bash CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 43b0148310ba hello-world "/hello" 16 minutes ago Exited (0) 9 minutes ago serene_poincare b60202284ace busybox "ping google.com" 3 hours ago Exited (0) 3 hours ago exciting_tharp 298176ed2948 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago zen_johnson 38f01afc355f hello-world "echo hi there" 4 hours ago Created distracted_austin b25255cc9ef7 hello-world "ls" 4 hours ago Created awesome_swirles b09147ec3aae busybox "ls" 4 hours ago Exited (0) 4 hours ago youthful_wu ab8b6c0bf713 busybox "echo hi there" 4 hours ago Exited (0) 4 hours ago wonderful_archimedes 9435b6d0c6f7 hello-world "/hello" 5 hours ago Exited (0) 5 hours ago xenodochial_kepler ``` Then, let's say we pick the seventh entry (second last) from the list. Using the container id, we can issue the following command to start the container again. ```bash docker start -a ab8b6c0bf713 hi there ``` One thing to note is that we cannot modify the start command for a container which has been already created. For example, ```bash docker start -a ab8b6c0bf713 echo bye there you cannot start and attach multiple containers at once ``` As can be observed, docker misinterprets the command and throws an error. ### Removing Stopped Containers To remove all containers, following is the command: ```bash docker system prune WARNING! This will remove: - all stopped containers - all networks not used by at least one container - all dangling images - all dangling build cache Are you sure you want to continue? [y/N] y Deleted Containers: 43b0148310bad8560734d780be5b7f7aac788b646a046efaa93e50d4558395d9 b60202284acedd38ed38988290017182071b2fc152ab14414dce96435a5ae749 298176ed29480b90d5ac928ec1d8b8c474c9dd04941c4fdf8f7387632a36d670 38f01afc355fc6bdc96dec59b560cfcce81302e8a3939f0e55bf48bafc2a10c7 b25255cc9ef76f1bdd6ca4317f388ebff7890b526f2817292b2dc4264fe7f7a1 b09147ec3aaeb26d8e396564ee2638178048da49b7d0623d40606c77be56bf6b ab8b6c0bf7138516fd84ccd78c3352515549df6012a90540720437443cf587c6 9435b6d0c6f71a5db9eb23f93a863a33a8b269e2179d1c7ccb71fb36a1899ee5 Total reclaimed space: 0B ``` As can be observed above, before removing all the stopped containers, docker outputs a warning and requests a confirmation from the user to actually remove the stopped containers. ### Retrieving Log Outputs Another way of getting the output from a container without using the `-a` flag with `docker start` is using the `docker logs` command. Specifically, below is the command to get logs from a container. ![](/files/3BO8Y74rEfjvjPeDmlFL) Following is the series of command that shows usage of `docker logs` command: ```bash docker create busybox echo hi there 1a75b9eec51c364c71d12cfbeb96d3e6adc6789a4551a2de6ae22a72fe3d954c docker start 1a75b9eec51c364c71d12cfbeb96d3e6adc6789a4551a2de6ae22a72fe3d954c 1a75b9eec51c364c71d12cfbeb96d3e6adc6789a4551a2de6ae22a72fe3d954c docker logs 1a75b9eec51c364c71d12cfbeb96d3e6adc6789a4551a2de6ae22a72fe3d954c hi there ``` ### Stopping Containers There are 2 ways of stopping a running container: ![](/files/oy9s7Aa4KW6tEsxpCOA4) Both the above commands are going to stop a running container. While both these commands kind of do the same thing, internally there is a difference between them. When `docker stop` command is issued, a hardware signal SIGTERM is sent to the primary process inside the concerned container. This message tells the container to shutdown on its own time. On the other hand, the `docker kill` command issues a SIGKILL signal to the primary process inside the concerned container. SIGKILL essentially means the conatiner has to shutdown right away without doing any additional work. Ideally, `docker stop` should be used to stop a container. If a container is non-responsive, we can use `docker kill` command instead. One thing to note about the `docker stop` command is that, when this command is executed and the concerned container does not stop automatically in 10 seconds, then docker will automatically fall back to executing `docker kill` command. Following is a series of commands which creates and start a busybox container. Then it outputs the logs from the container. Finally, we stop the running container. ```bash docker create busybox ping google.com d506eaabd695a57e27fcec70f1f3caae1b8f5006e40f668e5c2a95388ce6c793 docker start d506eaabd695a57e27fcec70f1f3caae1b8f5006e40f668e5c2a95388ce6c793 d506eaabd695a57e27fcec70f1f3caae1b8f5006e40f668e5c2a95388ce6c793 docker logs d506eaabd695a57e27fcec70f1f3caae1b8f5006e40f668e5c2a95388ce6c793 PING google.com (172.217.160.238): 56 data bytes 64 bytes from 172.217.160.238: seq=0 ttl=37 time=12.531 ms 64 bytes from 172.217.160.238: seq=1 ttl=37 time=15.300 ms 64 bytes from 172.217.160.238: seq=2 ttl=37 time=18.923 ms 64 bytes from 172.217.160.238: seq=3 ttl=37 time=16.998 ms 64 bytes from 172.217.160.238: seq=4 ttl=37 time=15.382 ms 64 bytes from 172.217.160.238: seq=5 ttl=37 time=16.754 ms 64 bytes from 172.217.160.238: seq=6 ttl=37 time=15.589 ms 64 bytes from 172.217.160.238: seq=7 ttl=37 time=14.521 ms 64 bytes from 172.217.160.238: seq=8 ttl=37 time=13.746 ms docker stop d506eaabd695a57e27fcec70f1f3caae1b8f5006e40f668e5c2a95388ce6c793 d506eaabd695a57e27fcec70f1f3caae1b8f5006e40f668e5c2a95388ce6c793 ``` ### Multi-Command Containers As an illustration, let's start running a new container with `redis-server` running inside it. Redis is an in memory data structure store. Following is the command to do so: ```bash docker run redis ``` #### Executing Commands in Running Containers After starting the container using the `redis` image, we now need to somehow start-up the the `redis-cli` also inside the container. For this, we would use the `docker exec` command: ![](/files/zqVyX6YWkVvzgxSFAe1r) Following is how to run `redis-cli` in the started container: ```bash docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES b025f927bfa2 redis "docker-entrypoint.s…" 27 minutes ago Up 27 minutes 6379/tcp flamboyant_sammet docker exec -it b025f927bfa2 redis-cli 127.0.0.1:6379> set myvalue 5 OK 127.0.0.1:6379> get myvalue "5" ``` ### Command Prompt in a Container There is another usecase for the `docker exec` command which is more commonly used. This usecase is getting shell or terminal access to a running container. In other words, this would be mean running shell commands inside of a container without running `docker exec` repeatedly. Following is the command for this: ```bash docker exec -it b025f927bfa2 sh # cd / # ls bin boot data dev etc home lib media mnt opt proc root run sbin srv sys tmp usr var # export b=5 # echo $b 5 # redis-cli 127.0.0.1:6379> # exit ``` `sh` is a command processor which allows to type commands in and have them be executed inside of that container. There are other command processors as listed below: ![](/files/Ag1e8PzPg1zoreBzJZrH) #### Starting a Shell We can also start a shell via the `docker run` command like below: ```bash docker run -it busybox sh / # ls bin dev etc home proc root sys tmp usr var / # echo hi there hi there / # exit ``` One disadvantage of starting the shell via the `docker run` command is that it does not allow to run the container's default process when starting up. 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