Navigating the Docker ecosystem can be confusing at the best of times.
I’ve been involved in numerous conversations where people have confused Indexes, Registries, Commits, diffs, pushes, Pods, Containers, Images… the list goes on.
I’ve put together these references to try and help with these confusions. Please get in touch if anything seems amiss, or you have any suggestions for improvements.
Reference is kept here.
Docker
| Container | A running instance of a Docker image |
| Image | A tagged history of layers make up an image |
| Layer | A set of file-level diffs. See diff |
| Privileged | Containers are privileged if they run with full root powers. Normally, root within the container has a reduced set of capabilities |
| Registry | A registry is a hosted service containing repositories of images, which responds to the Docker registry API |
| Swarm | Docker Swarm is a clustered set of Docker nodes connected and managed by a Swarm manager running on each node |
Docker vs Git
| Docker | Git | |
| Blob | Most often seen in the context of registries (API version 2) where the objects managed by the registry are stored in binary objects | The git index points to blobs that refer to content making up the repository’s history |
| Commit | Takes the differences in the container you reference to the last image, and creates a new layer. The added layer and all previous layers constitutes a new image | Takes the changes in your index and stores them in your local repository with a message |
| Diff | Gives you the files added, updated, or deleted in a layer | Gives a line-by-line diff of files between two revisions in the git repository’s history |
| History | The layers that make up an image (in order) constitute an image’s history | The ordered previous revisions in a repository |
| Hub | DockerHub is an index of images and Dockerfiles managed by Docker.inc. | GitHub is a popular central point of reference for software projects that use git |
| Index | Apparently deprecated term for a registry | A binary file in a git repository that stores references to all the blobs that make up a repository |
| Pull | Images are pulled from registries to your local host | Get a set of commits and apply them to your local repository |
| Push | Committed and tagged images can be pushed to registries | Commits can be pushed to remote repositories |
| Repository | A collection of images distinguished by tag, eg docker.io/ubuntu | A git project, ie the folder you might pull from a git remote |
| Remote | N/A, though if someone uses this term, they probably mean registry | A repository stored in another location, eg on GitHub or bitbucket.org |
| Revision | N/A | See commit |
| Tag | Tags are applied to repositories to distinguish different images, eg docker.io/ubuntu:14.04 is a different image from docker.io/ubuntu:15.04, but both are in the same repository | A reference to a git repository in a particular state |
Kubernetes
| Endpoint | IP and port that accepts TCP or UDP flows |
| Kube-proxy | Receives information about changes to services and endpoints |
| Kubelet | See Replication Controller |
| Replication Controller | Container supervisor. One of these runs on each host, ensuring the correct pods are running and in the appropriate number |
| Controller Manager | Orchestrates replication controllers |
| Pod | A grouping of containers that run on one host, and share volumes and a network stack (ie including IP and ports). Pods can run as one-offs, while long-running services should be spun up by replication controllers |
| Service | An abstracted endpoint for a set of pods or other endpoint |
OpenShift
| Build Controller | Component that manages the building of Docker images ready for deployment |
| Deployment Controller | Component that manages the deployment of Docker images to pods on nodes in the cluster |
| Image Stream | A set references to other images (and/or image streams). This provides a virtual view of related images, which allow operational control of events when any of the referenced image (and/or image streams) are changed. These events might trigger a rebuild or redeployment of a build. |
| Route | A DNS-resolveable endpoint that maps to an ip address and port |
| Image Stream Tag | Image Streams can be tagged in a similar way to Docker image tags |
Docker vs Kubernetes vs OpenShift
| Docker | Kubernetes | OpenShift | |
| Cluster | A cluster is a set of Nodes that run Docker Swarm | A Kubernetes Cluster is a set of master nodes and minions | An OpenShift Cluster is a set of OpenShift ‘master nodes’ plus a set of OpenShift nodes |
| Label | Name value pair applied to an object, eg an image or container | Name value pair applied to an object, eg pod or node | Name value pair applied to an object, eg route |
| Master | The Swarm Node acting as the elected master | The node or nodes that act as the cluster master, keeping track of centralised information using etcd nodes | The node or nodes that act as the cluster master, keeping track of centralised information using etcd nodes |
| Minion | N/A | Node on which Pods can be run | Rarely used, but would correspond to an OpenShift Node |
| Namespace | Kernel facility to allocate an isolated instance of a global resource, eg filesystem or network. Docker is partly a product that orchestrates these isolated components in a consumable way | Isolated sets of resources for management purposes | Isolated sets of resources for management purposes |
| Node | A host within a Swarm cluster | A host within a Kubernetes cluster | A host within an OpenShift cluster |
| Project | N/A | N/A | Extension of Kubernetes’ namespace concept with the addition of RBAC etc. |
| Service | Stable endpoint that forwards requests to (transient) containers | Stable endpoint that forwards requests to (transient) pods | Stable endpoint that forwards requests to (transient) pods |
zwischenzugs 
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