Node Js 8.11.1 2021 Download
Raffi Bramlett
A third, optional dimension (altitude) can also be included: key:ele (abbrev. for "elevation"). A node can also be defined as part of a particular layer=* or level=*, where distinct features pass over or under one another; say, at a bridge.
Nodes can be used on their own to define point features. When used in this way, a node will normally have at least one tag to define its purpose. Nodes may have multiple tags and/or be part of a relation. For example, a telephone box may be tagged simply with amenity=telephone, or could also be tagged with operator=*.
Where ways intersect at the same altitude, the two ways must share a node (for example, a road junction). If highways or railways cross at different heights without connecting they should not share a node (e.g. highway intersection with a bridge=*). Where ways cross at different heights they should be tagged with different layer=* or level=* values, or be tagged with location=* 'overground' or 'underground'. There are some exceptions to this rule, roads across dams are by current definition required to share a node with the waterway crossing the dam.
You can constrain a Pod so that it isrestricted to run on particular node(s),or to prefer to run on particular nodes.There are several ways to do this and the recommended approaches all uselabel selectors to facilitate the selection.Often, you do not need to set any such constraints; thescheduler will automatically do a reasonable placement(for example, spreading your Pods across nodes so as not place Pods on a node with insufficient free resources).However, there are some circumstances where you may want to control which nodethe Pod deploys to, for example, to ensure that a Pod ends up on a node with an SSD attached to it,or to co-locate Pods from two different services that communicate a lot into the same availability zone.
Adding labels to nodes allows you to target Pods for scheduling on specificnodes or groups of nodes. You can use this functionality to ensure that specificPods only run on nodes with certain isolation, security, or regulatoryproperties.
If you use labels for node isolation, choose label keys that the kubeletcannot modify. This prevents a compromised node from setting those labels onitself so that the scheduler schedules workloads onto the compromised node.
nodeSelector is the simplest recommended form of node selection constraint.You can add the nodeSelector field to your Pod specification and specify thenode labels you want the target node to have.Kubernetes only schedules the Pod onto nodes that have each of the labels youspecify.
nodeSelector is the simplest way to constrain Pods to nodes with specificlabels. Affinity and anti-affinity expands the types of constraints you candefine. Some of the benefits of affinity and anti-affinity include:
If you specify multiple expressions in a single matchExpressions field associated with aterm in nodeSelectorTerms, then the Pod can be scheduled onto a node onlyif all the expressions are satisfied (expressions are ANDed).
You can specify a weight between 1 and 100 for each instance of thepreferredDuringSchedulingIgnoredDuringExecution affinity type. When thescheduler finds nodes that meet all the other scheduling requirements of the Pod, thescheduler iterates through every preferred rule that the node satisfies and adds thevalue of the weight for that expression to a sum.
If there are two possible nodes that match thepreferredDuringSchedulingIgnoredDuringExecution rule, one with thelabel-1:key-1 label and another with the label-2:key-2 label, the schedulerconsiders the weight of each node and adds the weight to the other scores forthat node, and schedules the Pod onto the node with the highest final score.
When configuring multiple scheduling profiles, you can associatea profile with a node affinity, which is useful if a profile only applies to a specific set of nodes.To do so, add an addedAffinity to the args field of the NodeAffinity pluginin the scheduler configuration. For example:
The addedAffinity is applied to all Pods that set .spec.schedulerName to foo-scheduler, in addition to theNodeAffinity specified in the PodSpec.That is, in order to match the Pod, nodes need to satisfy addedAffinity andthe Pod's .spec.NodeAffinity.
Inter-pod affinity and anti-affinity allow you to constrain which nodes yourPods can be scheduled on based on the labels of Pods already running on thatnode, instead of the node labels.
Inter-pod affinity and anti-affinity rules take the form "thisPod should (or, in the case of anti-affinity, should not) run in an X if that Xis already running one or more Pods that meet rule Y", where X is a topologydomain like node, rack, cloud provider zone or region, or similar and Y is therule Kubernetes tries to satisfy.
If the current Pod being scheduled is the first in a series that have affinity to themselves,it is allowed to be scheduled if it passes all other affinity checks. This is determined byverifying that no other pod in the cluster matches the namespace and selector of this pod,that the pod matches its own terms, and the chosen node matches all requested topologies.This ensures that there will not be a deadlock even if all the pods have inter-pod affinityspecified.
The affinity rule specifies that the scheduler is allowed to place the example Podon a node only if that node belongs to a specific zonewhere other Pods have been labeled with security=S1.For instance, if we have a cluster with a designated zone, let's call it "Zone V,"consisting of nodes labeled with topology.kubernetes.io/zone=V, the scheduler canassign the Pod to any node within Zone V, as long as there is at least one Pod withinZone V already labeled with security=S1. Conversely, if there are no Pods with security=S1labels in Zone V, the scheduler will not assign the example Pod to any node in that zone.
The anti-affinity rule specifies that the scheduler should try to avoid scheduling the Podon a node if that node belongs to a specific zonewhere other Pods have been labeled with security=S2.For instance, if we have a cluster with a designated zone, let's call it "Zone R,"consisting of nodes labeled with topology.kubernetes.io/zone=R, the scheduler should avoidassigning the Pod to any node within Zone R, as long as there is at least one Pod withinZone R already labeled with security=S2. Conversely, the anti-affinity rule does not impactscheduling into Zone R if there are no Pods with security=S2 labels.
One example use case is to ensure Pods go to the topology domain (node, zone, etc) where only Pods from the same tenant or team are scheduled in.In other words, you want to avoid running Pods from two different tenants on the same topology domain at the same time.
Inter-pod affinity and anti-affinity can be even more useful when they are used with higherlevel collections such as ReplicaSets, StatefulSets, Deployments, etc. Theserules allow you to configure that a set of workloads shouldbe co-located in the same defined topology; for example, preferring to place two relatedPods onto the same node.
For example: imagine a three-node cluster. You use the cluster to run a web applicationand also an in-memory cache (such as Redis). For this example, also assume that latency betweenthe web application and the memory cache should be as low as is practical. You could use inter-podaffinity and anti-affinity to co-locate the web servers with the cache as much as possible.
In the following example Deployment for the Redis cache, the replicas get the label app=store. ThepodAntiAffinity rule tells the scheduler to avoid placing multiple replicaswith the app=store label on a single node. This creates each cache in aseparate node.
The following example Deployment for the web servers creates replicas with the label app=web-store.The Pod affinity rule tells the scheduler to place each replica on a node that has a Podwith the label app=store. The Pod anti-affinity rule tells the scheduler never to placemultiple app=web-store servers on a single node.
nodeName is a more direct form of node selection than affinity ornodeSelector. nodeName is a field in the Pod spec. If the nodeName fieldis not empty, the scheduler ignores the Pod and the kubelet on the named nodetries to place the Pod on that node. Using nodeName overrules usingnodeSelector or affinity and anti-affinity rules.
You can use topology spread constraints to control how Podsare spread across your cluster among failure-domains such as regions, zones, nodes, or among any othertopology domains that you define. You might do this to improve performance, expected availability, oroverall utilization.
A network node is a connection point in a communications network. Each node is an endpoint for data transmissions or redistribution. Nodes have either a programmed or engineered capability to recognize, process and forward transmissions to other network nodes.
In a computer network, nodes can be physical networked devices, such as modems, PCs and printers. These devices recognize transmissions from other nodes and forward them to other nodes. A node checks for identification, such as an IP address, to grant access to the node.
Print request. An employee sends a print request from a computer to a printer located in another part of the office. The employee's computer is a node on the network. The request travels over the network and through a series of other nodes -- a router, for example -- on the company LAN. The request reaches the printer, also a node; it processes the request and completes the printing job.
Base station controller. This is a node on a cellular network that provides intelligent network services to devices. The base station controller sits between the cell sites and mobile switching center, which are also nodes on the cell network. Base station controllers determine how cell signals should be routed through the network.
Peer-to-peer mesh network. A peer-to-peer mesh network lets mobile devices communicate information without Wi-Fi or cellular service. In a mesh network topology, every node connects to every other node. Cellphones act as nodes and extend their signals to other cellphones in the network that may be experiencing a service outage. IBM's The Weather Company is using this approach to transmit critical information when other networks may be down.
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