Containerization

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Containerization Tool Ecosystem

  • Kubernetes - container orchestration system that manages containerized applications across multiple hosts
    • Self-Healing: Kubernetes continuously monitors the state of pods and nodes and can restart or replace containers that fail, migrate containers when nodes die, and kill containers that don't respond to user-defined health checks.
    • Helm charts package all the necessary components needed to run an application or service on Kubernetes.
  • Docker Swarm - turns a pool of Docker hosts into a single, virtual Docker host
  • Podman - run containers without daemon, without root access.
    • Manage groups of containers together in pods like kubernetes
    • podman-compose compatible with docker-compose
  • Colima - Docker Desktop replacement. Container runtimes on macOS (and Linux) with minimal setup. 16k+ stars on github
  • Amazon Elastic Container service, and Azure Container Instances
  • BuildKit
    • Parallelize run steps that do no depend on eachother
    • Use secrets during the build process without leaving traces of those secrets in the final image

General

  • Containerization stands in contrast to traditional architectures:
    • Monolithic - easiest to do at first, difficult to scale
    • Service-oriented - smaller, loosely-coupled services developed deployed and scaled independently
    • Microservices architectures - SOA + well defined APIs
  • Less secure than virtual machines as containers share the host system’s kernel, whereas VMs provide hardware-level virtualization.
    • If the kernel is compromised, so are the containers.
  • Containers don't include OSes and are lightwieght.
  • Containers build for one CPU architecture can be run on another using QEMU (open-source machine emulator and virtualizer). Beware emulation overhead, i.e., translating instructions from one architecture to another at runtime.

Images/Containers lifecycle

  • Dockerfile instructions are only executed during image build process. Results in a Docker image which is a static snapshot of the environment and code as defined in Dockerfile
  • When you docker run, docker creates a container based on that static image.
  • Containers do no autoupdate - you must rebuild the image and recreate the containers from the updated image
  • Run docker build <dockerfile> to rebuild image or docker compose build in a directory with a docker-compose.yml to rebuild all the images/containers in your docker compose project.


Terminology

  • Daemon/Engine/Server - a process running on a host os/system
  • Image - READ-ONLY: image does not have state and never changes.
  • Container- A "stateful" instance of a docker image
  • Layer - A modification to the image, represented by an instruction in the Dockerfile
    • Caching- When an image is updated or rebuilt, only layers that change need to be updated, and unchanged layers are cached locally. This is part of why Docker images are so fast and lightweight.
  • Dockerfile - All the commands you would normally execute manually in order to build a Docker image
  • Docker Hub - Docker certified images/template hosting, with SECVULN scanning
    • Official images vs open source images
    • also Github Container Repository (ghcr.io), Red Hat Quay (quay.io), AWS Elastic Container Registry (ECR), or Google Container Registry (GCR)
  • Compose - Defining and running multi-container Docker applications
  • Docker Desktop - includes engine, cli client, compose, content trust, kubernetes, credential helper

Alpine Linux

  • Alpine Linux's combination of a small footprint, security features, and efficiency has made it a popular choice for Docker containers
  • Lightweight, security-oriented Linux distribution based on musl libc (a lightweight standard library for C language) and BusyBox
  • Alpine Linux does not derive from one of the major families like Debian or Red Hat but is independently developed, but rather created by Natanael Copa in 2005 as a fork of the LEAF Project (Linux Embedded Appliance Framework)
  • Minimal size 5 MB base image!!!
  • You probably shouldn't use Alpine for Python projects, instead use the slim Docker image versions that are still based on Debian, but are smaller. - source: tiangolo
    • Alpine is more useful for other languages where you build a static binary in one Docker image stage (using multi-stage Docker building) and then copy it to a simple Alpine image, and then just execute that binary. For example, using Go. But for Python, as Alpine doesn't use the standard tooling used for building Python extensions, when installing packages, in many cases Python (pip) won't find a precompiled installable package (a "wheel") for Alpine.

Bitnami

Bitnami containers, including the Python container, are designed to be lightweight and secure, focusing on running applications. As such, they often do not include unnecessary packages, tools like SSH, or even a full shell environment that you might be accustomed to in standard Linux distributions. This design choice helps minimize the attack surface and the size of the container image.

Low-level implementation of containerization

  • Namespaces - within Linux kernel, isolates and virtualizes the system resources, restricts processes within the namespace to only interact with other processes in the same namespace
  • Control groups - limit and isolate resource usage (CPU, memory, I/O, network
  • Union file system - allowing files and directories of separate file systems, known as layers, to be transparently overlaid to form a single coherent file system.


Docker CLI Commands

Version

  • docker version - will give you client AND server version info

Info

  • docker info - more verbose docker server information

List installed Images

  • docker images -a - list the installed images, -a includes the exited ones

List containers

  • docker ps -a - running process image, age, status, name, and port information
  • -a flag lists exited containers as well
  • --size flag lists container size, i.e., disk space
    • Actual size: The size utilized by the writable container layer consists of the container’s filesystem and any modifications made
    • Virtual Size: combined size of all the container's layers, which include any shares, base pictures, and additional layers
  • docker ps -a --format 'Template:.ID' | xargs docker rm

top

  • docker stats - Resource utilization like top broken down by container

Logs

  • docker logs [OPTIONS] CONTAINER - --details, -f, -tail n, --timestamps, --until

Exec

  • docker exec -it HEXADECIMAL bash - ssh into container, just do this to begin with and keep a tmux open with it.

Pull

  • docker pull - pull from dockerhub or wherever
  • docker pull nvcr.io/nvidia/digits:18.06
  • docker pull nvidia/caffe

Remove Container

  • docker rm Container_ID_or_Name - remove container
  • docker rm $(docker container ls -q -a)

Remove Image

  • docker rmi $(docker images -a -q) - remove all images

History

  • docker history --no-trunc IMAGE_NAME - Show all layers of an image in reverse chronological order (the last layer being the one on top).

Run

  • For interactive container session, usage is docker run -it <image> <command>
    • <-it: This is a combination of -i and -t. -i keeps STDIN open even if not attached, and -t allocates a pseudo-TTY, making the terminal interactive.
    • command could be sh or bash
  • Examples:
    • docker run --gpus all -it --name tensorflow_1910_py3 -d --net=host -v /home/colettace/projects:/projects --ipc=host --ulimit memlock=-1 nvcr.io/nvidia/tensorflow:19.10-py3
    • docker run --runtime=nvidia --name digits -d -p 5000:5000 -v /jobs:/jobs -v /datasets:/datasets -it nvidia/digits
    • docker run -P - uppercase P publishes all ports that are exposed (?)
    • docker run --entrypoint /bin/sh -it myimage:latest -c "cat /app/config/app.conf" Override entrypoint for debugging purposes

Login

  • Log in with your Docker ID or email address to push and pull images from Docker Hub

Search

  • docker search --filter=is-official=true nginx - show official nginx image

Manifest

  • docker manifest inspect <image_name> - see all available manifests and their architectures.
  • A manifest list allows you to use one name to refer to the same image built for multiple architectures

Build

  • <cdoe>docker build --tag myapp:latest .
  • --squash Squash layers to save space?

When you need secrets to build

  • Do not use ARG to pass secrets, which may leave sensitive information in image layers
  • docker build --secret id=mysecret,src=/path/to/secret/file.txt -t myapp:latest . - build with a secret
    • RUN --mount=type=secret,id=mysecret cat /run/secrets/mysecret - Use the secret without exposing it in the image
  • Use when
    • When your build requires pulling dependencies from private repositories.
    • When you need to use private keys for SSH access or to decrypt files during the build
    • When your build process involves accessing APIs that require authentication

.dockerignore

  • tells Docker which files and directories to ignore when building an image
.git
.gitignore
Dockerfile*
*.md
node_modules
temp/

Prune

  • prune images, containers, volumes, networks, and build cache

Environment Vars

# Enable Docker BuildKit
export DOCKER_BUILDKIT=1


cp

  • docker cp /host/directory/path container_name:/container/directory/path
  • -a archive
  • -L follow links

Dockerfile Syntax

FROM

  • Initialize new build stage, specifies base image
  • Mandatory first non-comment instruction
  • could also be FROM scratch

LABEL

  • Adds metadata to an image, like the maintainer, version, or any other key-value pairs you wish to include.
  • Replaces deprecated MAINTAINER statement

RUN

  • Executes any commands on top of the current image layer and commits the results
  • Install software packages, build code, or change file system contents

CMD

  • defaults for executing a container
  • There can be only one of these in a Dockerfile

COPY

  • copy from source working directory in current build context (where you run docker build) or build container, to destination filesystem

ADD

  • like COPY but with url and tarball auto-extraction support
  • Avoid since downloading from URL could introduce unexpected behavior
  • Use RUN wget or RUN curl to provide more control over the download process (e.g., checksum validation)

ENV

  • Set environment variables
  • Can be overridden at runtime using -e

EXPOSE

  • Exposes a port to be accessed internally by other containers within app.
  • Does not actually publish the port to the outside, or make a service available outside Docker environment.
  • Not strictly necessary since two containers on the same network within Docker Compose will be able to listen to any port regardless
  • Helps to be explicit, helps document intentions, helps some orchestration tools

ENTRYPOINT

  • Configures a container that will run as an executable. Command line arguments to docker run <image> will be appended.

USER

  • specify username/UID, otherwise it's root. Will be the user of any command run by RUN, CMD and ENTRYPOINT instructions

VOLUME

  • Persist data outside containers on host OS, because data within containers is ephemeral.
  • Creates a mount point with the specified name and marks it as holding externally mounted volumes from the native host or other containers.
  • Critical for database
  • Containers themselves are stateless; it's the volumes that hold the state

WORKDIR

  • Sets the target directory inside the container
  • Change the current working directory for the duration of the Dockerfile
  • Sets the working directory for any RUN, CMD, ENTRYPOINT, COPY, and ADD instruction
  • Creates the dir in the container if it doesn't exist

ARG

  • Defines a variable that users can pass at build-time to the builder with the docker build command using the --build-arg <varname>=<value> flag.
  • Does not add a layer to the image.
  • Variables can then be used using the traditional BASH syntax ${variable}
  • Validate like so:
    • RUN if [ "$config" != "expected_value" ]; then echo "Invalid config value" && exit 1; fi
    • RUN \[ "${variable}" == "true" \] && ...
  • ARG values aren't available in the final image like ENV values are
  • Security: ARG values can still be seen in the intermediate layers of the build process and potentially in the Dockerfile itself

STOPSIGNAL

  • How you indicate the stop signal that your application or main process is configured to handle for a graceful shutdown.
  • Default is SIGTERM followed by SIGKILL when you hit Control-C again or after 10 second grace period passes.

Others

  • ONBUILD
  • HEALTHCHECK
  • SHELL

Dockerfile workflow

  • Try to order instructions to optimize build cache usability

Multistage builds

  • reduces final image size as well as reduces attack surface by excluding unnecessary tools
  • Use multiple FROM statements in Dockerfile, give earlier ones aliases using the AS keyword
  • COPY --from=builder /app/myapp /app/myapp

Docker Compose

  • Installation - Included with Docker desktop for Windows and MacOS, otherwise download binary for linux based on CPU architecture
  • Can define volumes, configs, secrets at top-level, otherwise define at service level
  • Service names as hostnames - Containers within the same network can reach and communicate with each other using the service names as hostnames.
  • Merge multiple Compose files
    • e.g., production.yml for production-appropriate configuration
  • Profiles: A service with no profile specified means it's always active, otherwise must specify when running up command
  • Can interpolate variables into values used in compose files at runtime using bash-like syntax
    • $VARIABLE
    • ${VARIABLE}
    • ${VARIABLE-default} - "-" dash delimiter specifies default value only if VARIABLE is unset
    • ${VARIABLE:-default} - ":-" colon-dash delimiter specifies default value if VARIABLE is unset OR empty
    • ${VARIABLE?err_msg} - "?" error out with err_msg if VARIABLE is unset (":?" if unset or empty)
    • Interpolation can be nested: ${VARIABLE:-${FOO:-default}}
    • $$ - a literal dollarsign
    • Can't interpolate YAML keys, only values

Compose file syntax

services

  • services - key is the service name, values is the service definition
  • platform: linux/amd64 - os/arch/variant - specify if the image is specific to a platform
  • image - no build step necessary if you use an image
  • build
    • Either path to build context, or break out into details
    • context - path is relative to current compose file, else defaults to .
    • dockerfile: path/to.Dockerfile - look for a specific named dockerfile, otherwise just look for a file named Dockerfile
    • If list both image and build, will try to pull image first before building if that fails
  • ports: [HOST IP:]host_port:container_port - ports can also be ranges
  • depends_on - expresses startup & shutdown dependencies between services
  • environment - set env vars inside container
    • Use "true", "false", "yes", "no", any boolean values should be quoted, otherwise will be converted by YAML parser
    • can use YAML map syntax ENV_VAR: value or array syntax with one dash per line - ENV_VAR=value
  • command: <linux shell command> - overrides the default command declared by container image within dockerfile CMD
  • volumes
    • directories on host machine's filesystem mounted into container
    • HOST_PATH or top-level volume name:CONTAINER_PATH:ACCESS_MODE - access modes are rw, ro, z, Z SELinux shared and unshared with other containers respectively.
    • Creates the host path if not there by default
  • profiles - only run these services when I explicitly ask for them in my docker compose up command
  • container_name - specify a custom container name, rather the default generated name <project_name>_<service_name>_<instance_number>


others

  • networks - services communicate with each other through networks. Establish an IP route between containers to connect services
    • specify a default network
  • volumes - How services store and share persistent data. Could be high-level filesystem mount, bypasses union filesystem
    • If declared at top-level, volumes can be reused across multiple services
  • configs - files mounted into the container
  • secrets - flavor of configuration data
  • Project - project name set with top-level name attribute
    • Can then expose COMPOSE_PROJECT_NAME in services/<SERVICE NAME>/environment yaml section which will then get pushed to env vars within container


Docker Compose CLI Commands

Up

--profile

  • docker compose up --profile <profile name> -f docker-compose.custom.yml
  • Note --profile != -p - this will fail silently!!

Overrides

  • docker compose -f docker-compose.yml -f production.yml up -d - overrides are done in order, i.e., LIFO

detached mode

  • docker compose up -d - send process into the background
  • docker compose stop - stops the containers
  • docker compose down stops the containers and also removes them along with any networks that were created
    • can help remove any orphans containers from previous runs that don't stop when told to for some reason

Exec

  • docker compose exec stac-browser /bin/sh - exec into the raw image

Build

  • docker compose build --no-cache - force rebuild from scratch for all images
  • docker compose build <service_name> - only rebuild the image that corresponds to service_name in your docker-compose.yml.

Verbose

  • docker compose --verbose up -f docker-compose.custom.yml

logs

  • docker compose logs

Config

  • docker compose config - outputs the final configuration derived from your docker-compose.yml and .env files, after all variable substitutions

Env Vars

  • DOCKER_CLI_EXPERIMENTAL=enabled
  • COMPOSE_DOCKER_CLI_BUILD=1 - make Docker Compose use the Docker CLI directly for image building, which might provide more detailed output

Install/Enable Docker Server (Daemon)

  • sudo systemctl start docker
    • sudo systemctl enable docker - for CentOS7
  • journalctl -u docker - daemon log for CentOS7

Terraform using Docker

provider "docker" {
  # Provider configuration
}

resource "docker_image" "nginx" {
  name         = "nginx:latest"
  keep_locally = false
}

resource "docker_container" "nginx" {
  image = docker_image.nginx.latest
  name  = "nginx-example"
  ports {
    internal = 80
    external = 8080
  }
}

NVIDIA Images

  • ngc.nvidia.com - NGC registry page
  • On website registry page, generate NGC API key then store it somewhere safe
    • I put it in a file in the home directory
    • not a big deal if you lose it, just generate a new one, old key become invalid
  • then, on server: docker login nvcr.io - user $oauthtoken, password use NGC API key

Reference

Retrieved from "https://chriscoletta.com/index.php?title=Containerization&oldid=4292"