github/kubernetes
1
0
Fork 0
mirror of https://github.com/k3s-io/kubernetes.git synced 2025-09-12 12:48:51 +00:00
Code Issues Projects Releases Wiki Activity

Separated user, dev, and design docs.

Browse Source 
Renamed: logging.md -> devel/logging.m
Renamed: access.md -> design/access.md
Renamed: identifiers.md -> design/identifiers.md
Renamed:    labels.md -> design/labels.md
Renamed:    namespaces.md -> design/namespaces.md
Renamed:    security.md -> design/security.md
Renamed:    networking.md -> design/networking.md

Added abbreviated user user-focused document in place of most moved docs.

Added docs/README.md explains how docs are organized.
Added short, user-oriented documentation on labels
Added a glossary.
Fixed up some links.
This commit is contained in:
Eric Tune
2014-10-16 14:45:16 -07:00
parent a18cdac616
commit c47693c0d5
16 changed files with 656 additions and 452 deletions
Download Patch File Download Diff File Expand all files Collapse all files

94
docs/identifiers.md
View File

@@ -1,90 +1,8 @@
# Identifiers and Names in Kubernetes
# Identifiers
All objects in the Kubernetes REST API are identified by a Name and a UID.
A summarization of the goals and recommendations for identifiers in Kubernetes. Described in [GitHub issue #199](https://github.com/GoogleCloudPlatform/kubernetes/issues/199).
## Names
Names are user-provided. Only one object of a given kind can have a given name at a time. But if you delete an object, you can make a new object with the same name. Names are the used to refer to an object in a resource URL, such as `/api/v1beta3/pods/some.name`. Names may be up to maximum length of 253 characters and consist of alphanumeric characters, `-`, and `.`. See the [identifiers design doc](design/identifiers.md) for the precise syntax rules for names.
## Definitions
UID
: A non-empty, opaque, system-generated value guaranteed to be unique in time and space; intended to distinguish between historical occurrences of similar entities.
Name
: A non-empty string guaranteed to be unique within a given scope at a particular time; used in resource URLs; provided by clients at creation time and encouraged to be human friendly; intended to facilitate creation idempotence and space-uniqueness of singleton objects, distinguish distinct entities, and reference particular entities across operations.
[rfc1035](http://www.ietf.org/rfc/rfc1035.txt)/[rfc1123](http://www.ietf.org/rfc/rfc1123.txt) label (DNS_LABEL)
: An alphanumeric (a-z, A-Z, and 0-9) string, with a maximum length of 63 characters, with the '-' character allowed anywhere except the first or last character, suitable for use as a hostname or segment in a domain name
[rfc1035](http://www.ietf.org/rfc/rfc1035.txt)/[rfc1123](http://www.ietf.org/rfc/rfc1123.txt) subdomain (DNS_SUBDOMAIN)
: One or more rfc1035/rfc1123 labels separated by '.' with a maximum length of 253 characters
[rfc4122](http://www.ietf.org/rfc/rfc4122.txt) universally unique identifier (UUID)
: A 128 bit generated value that is extremely unlikely to collide across time and space and requires no central coordination
## Objectives for names and UIDs
1. Uniquely identify (via a UID) an object across space and time
2. Uniquely name (via a name) an object across space
3. Provide human-friendly names in API operations and/or configuration files
4. Allow idempotent creation of API resources (#148) and enforcement of space-uniqueness of singleton objects
5. Allow DNS names to be automatically generated for some objects
## General design
1. When an object is created via an API, a Name string (a DNS_SUBDOMAIN) must be specified. Name must be non-empty and unique within the apiserver. This enables idempotent and space-unique creation operations. Parts of the system (e.g. replication controller) may join strings (e.g. a base name and a random suffix) to create a unique Name. For situations where generating a name is impractical, some or all objects may support a param to auto-generate a name. Generating random names will defeat idempotency.
* Examples: "guestbook.user", "backend-x4eb1"
2. When an object is created via an api, a Namespace string (a DNS_SUBDOMAIN? format TBD via #1114) may be specified. Depending on the API receiver, namespaces might be validated (e.g. apiserver might ensure that the namespace actually exists). If a namespace is not specified, one will be assigned by the API receiver. This assignment policy might vary across API receivers (e.g. apiserver might have a default, kubelet might generate something semi-random).
* Example: "api.k8s.example.com"
3. Upon acceptance of an object via an API, the object is assigned a UID (a UUID). UID must be non-empty and unique across space and time.
* Example: "01234567-89ab-cdef-0123-456789abcdef"
## Case study: Scheduling a pod
Pods can be placed onto a particular node in a number of ways. This case
study demonstrates how the above design can be applied to satisfy the
objectives.
### A pod scheduled by a user through the apiserver
1. A user submits a pod with Namespace="" and Name="guestbook" to the apiserver.
2. The apiserver validates the input.
1. A default Namespace is assigned.
2. The pod name must be space-unique within the Namespace.
3. Each container within the pod has a name which must be space-unique within the pod.
3. The pod is accepted.
1. A new UID is assigned.
4. The pod is bound to a node.
1. The kubelet on the node is passed the pod's UID, Namespace, and Name.
5. Kubelet validates the input.
6. Kubelet runs the pod.
1. Each container is started up with enough metadata to distinguish the pod from whence it came.
2. Each attempt to run a container is assigned a UID (a string) that is unique across time.
* This may correspond to Docker's container ID.
### A pod placed by a config file on the node
1. A config file is stored on the node, containing a pod with UID="", Namespace="", and Name="cadvisor".
2. Kubelet validates the input.
1. Since UID is not provided, kubelet generates one.
2. Since Namespace is not provided, kubelet generates one.
1. The generated namespace should be deterministic and cluster-unique for the source, such as a hash of the hostname and file path.
* E.g. Namespace="file-f4231812554558a718a01ca942782d81"
3. Kubelet runs the pod.
1. Each container is started up with enough metadata to distinguish the pod from whence it came.
2. Each attempt to run a container is assigned a UID (a string) that is unique across time.
1. This may correspond to Docker's container ID.
## UIDs
UID are generated by Kubernetes. Every object created over the whole lifetime of a Kubernetes cluster has a distinct UID.