mirror of https://github.com/k3s-io/k3s
Fix some typos from my read-through
Justin Santa Barbara
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b3a4b1853d
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@ -37,7 +37,7 @@ This document provides high-level insight into how Kubernetes works on AWS and
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maps to AWS objects. We assume that you are familiar with AWS.
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We encourage you to use [kube-up](../getting-started-guides/aws.md) (or
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[CloudFormation](../getting-started-guides/aws-coreos.md) to create clusters on
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[CloudFormation](../getting-started-guides/aws-coreos.md)) to create clusters on
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AWS. We recommend that you avoid manual configuration but are aware that
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sometimes it's the only option.
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@ -63,7 +63,7 @@ kube-proxy relays traffic between the nodes etc).
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By default on AWS:
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* Instances run Ubuntu 15.04 (the official AMI). It includes a sufficiently
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modern kernel that parise well with Docker and doesn't require a
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modern kernel that pairs well with Docker and doesn't require a
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reboot. (The default SSH user is `ubuntu` for this and other ubuntu images.)
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* By default we run aufs over ext4 as the filesystem / container storage on the
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nodes (mostly because this is what GCE uses).
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@ -73,39 +73,36 @@ kube-up.
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### Storage
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AWS supports persistent volumes by using [Elastic Block Store
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(EBS)](../user-guide/volumes.md#awselasticblockstore). These can then be
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AWS supports persistent volumes by using [Elastic Block Store (EBS)](../user-guide/volumes.md#awselasticblockstore). These can then be
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attached to pods that should store persistent data (e.g. if you're running a
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database).
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By default, nodes in AWS use `[instance
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storage](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/InstanceStorage.html)'
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By default, nodes in AWS use [instance storage](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/InstanceStorage.html)
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unless you create pods with persistent volumes
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`[(EBS)](../user-guide/volumes.md#awselasticblockstore)`. In general,
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Kubernetes containers do not have persistent storage unless you attach a
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persistent volume, and so nodes on AWS use instance storage. Instance
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storage is cheaper, often faster, and historically more reliable. This does
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mean that you should pick an instance type that has sufficient instance
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storage, unless you can make do with whatever space is left on your root
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partition.
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[(EBS)](../user-guide/volumes.md#awselasticblockstore). In general, Kubernetes
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containers do not have persistent storage unless you attach a persistent
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volume, and so nodes on AWS use instance storage. Instance storage is cheaper,
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often faster, and historically more reliable. This does mean that you should
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pick an instance type that has sufficient instance storage, unless you can make
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do with whatever space is left on your root partition.
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Note: Master uses a persistent volume ([etcd](architecture.html#etcd)) to track
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its state but similar to the nodes, container are mostly run against instance
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Note: The master uses a persistent volume ([etcd](architecture.md#etcd)) to track
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its state but similar to the nodes, containers are mostly run against instance
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storage, except that we repoint some important data onto the peristent volume.
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The default storage driver for Docker images is aufs. Passing the environment
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variable `DOCKER_STORAGE=btrfs` is also a good choice for a filesystem. btrfs
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The default storage driver for Docker images is aufs. Specifying btrfs (by passing the environment
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variable `DOCKER_STORAGE=btrfs` to kube-up) is also a good choice for a filesystem. btrfs
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is relatively reliable with Docker and has improved its reliability with modern
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kernels. It can easily span multiple volumes, which is particularly useful
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when we are using an instance type with multiple ephemeral instance disks.
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### AutoScaling
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Nodes (except for the master) are run in an
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`[AutoScalingGroup](http://docs.aws.amazon.com/AutoScaling/latest/DeveloperGuide/AutoScalingGroup.html)
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Nodes (but not the master) are run in an
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[AutoScalingGroup](http://docs.aws.amazon.com/AutoScaling/latest/DeveloperGuide/AutoScalingGroup.html)
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on AWS. Currently auto-scaling (e.g. based on CPU) is not actually enabled
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([#11935](http://issues.k8s.io/11935)). Instead, the auto-scaling group means
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that AWS will relaunch any non-master nodes that are terminated.
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that AWS will relaunch any nodes that are terminated.
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We do not currently run the master in an AutoScalingGroup, but we should
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([#11934](http://issues.k8s.io/11934)).
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@ -134,9 +131,9 @@ pods.
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ELB has some restrictions: it requires that all nodes listen on a single port,
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and it acts as a forwarding proxy (i.e. the source IP is not preserved). To
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work with these restrictions, in Kubernetes, `[LoadBalancer
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services](../user-guide/services.html#type-loadbalancer)` are exposed as
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`[NodePort services](../user-guide/services.html#type-nodeport)`. Then
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work with these restrictions, in Kubernetes, [LoadBalancer
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services](../user-guide/services.html#type-loadbalancer) are exposed as
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[NodePort services](../user-guide/services.html#type-nodeport). Then
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kube-proxy listens externally on the cluster-wide port that's assigned to
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NodePort services and forwards traffic to the corresponding pods. So ELB is
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configured to proxy traffic on the public port (e.g. port 80) to the NodePort
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@ -155,18 +152,18 @@ will likely have to open the port in the node security group
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kube-proxy sets up two IAM roles, one for the master called
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[kubernetes-master](../../cluster/aws/templates/iam/kubernetes-master-policy.json)
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and one for the non-master nodes called
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and one for the nodes called
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[kubernetes-minion](../../cluster/aws/templates/iam/kubernetes-minion-policy.json).
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The master is responsible for creating ELBs and configuring them, as well as
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setting up advanced VPC routing. Currently it has blanket permissions on EC2,
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along with rights to create and destroy ELBs.
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The (non-master) nodes do not need a lot of access to the AWS APIs. They need to download
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The nodes do not need a lot of access to the AWS APIs. They need to download
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a distribution file, and then are responsible for attaching and detaching EBS
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volumes from itself.
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The (non-master) node policy is relatively minimal. The master policy is probably overly
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The node policy is relatively minimal. The master policy is probably overly
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permissive. The security concious may want to lock-down the IAM policies
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further ([#11936](http://issues.k8s.io/11936)).
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@ -198,9 +195,9 @@ The kube-up script does a number of things in AWS:
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* Creates an S3 bucket (`AWS_S3_BUCKET`) and then copies the Kubernetes distribution
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and the salt scripts into it. They are made world-readable and the HTTP URLs
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are passed to instances; this is how Kubernetes code gets onto the machines.
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* Creates two IAM profiles based on templates in `cluster/aws/templates/iam`:
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* `kubernetes-master` is used by the master node
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* `kubernetes-minion` is used by non-master nodes.
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* Creates two IAM profiles based on templates in [cluster/aws/templates/iam](../../cluster/aws/templates/iam):
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* `kubernetes-master` is used by the master
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* `kubernetes-minion` is used by nodes.
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* Creates an AWS SSH key named `kubernetes-<fingerprint>`. Fingerprint here is
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the OpenSSH key fingerprint, so that multiple users can run the script with
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different keys and their keys will not collide (with near-certainty). It will
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@ -215,22 +212,22 @@ one there. (With the default ubuntu images, if you have to SSH in: the user is
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* Creates a subnet (with a CIDR of 172.20.0.0/24) in the AZ `KUBE_AWS_ZONE`
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(defaults to us-west-2a). Currently, each Kubernetes cluster runs in a
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single AZ on AWS. Although, there are two philosophies in discussion on how to
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achieve High Availability (HA):
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achieve High Availability (HA):
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* cluster-per-AZ: An independent cluster for each AZ, where each cluster
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is entirely separate.
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* cross-AZ-clusters: A single cluster spans multiple AZs.
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is entirely separate.
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* cross-AZ-clusters: A single cluster spans multiple AZs.
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The debate is open here, where cluster-per-AZ is discussed as more robust but
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cross-AZ-clusters are more convenient.
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cross-AZ-clusters are more convenient.
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* Associates the subnet to the route table
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* Creates security groups for the master node (`kubernetes-master-<clusterid>`)
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and the non-master nodes (`kubernetes-minion-<clusterid>`)
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* Creates security groups for the master (`kubernetes-master-<clusterid>`)
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and the nodes (`kubernetes-minion-<clusterid>`)
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* Configures security groups so that masters and nodes can communicate. This
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includes intercommunication between masters and nodes, opening SSH publicly
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for both masters and nodes, and opening port 443 on the master for the HTTPS
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API endpoints.
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* Creates an EBS volume for the master node of size `MASTER_DISK_SIZE` and type
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* Creates an EBS volume for the master of size `MASTER_DISK_SIZE` and type
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`MASTER_DISK_TYPE`
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* Launches a master node with a fixed IP address (172.20.0.9) that is also
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* Launches a master with a fixed IP address (172.20.0.9) that is also
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configured for the security group and all the necessary IAM credentials. An
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instance script is used to pass vital configuration information to Salt. Note:
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The hope is that over time we can reduce the amount of configuration
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@ -251,17 +248,17 @@ is not required.
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If attempting this configuration manually, I highly recommend following along
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with the kube-up script, and being sure to tag everything with a
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`KubernetesCluster`=`<clusterid>` tag. Also, passing the right configuration
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options to Salt when not using the script is tricky: the plan here is to
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simplify this by having Kubernetes take on more node configuration, and even
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potentially remove Salt altogether.
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with the kube-up script, and being sure to tag everything with a tag with name
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`KubernetesCluster` and value set to a unique cluster-id. Also, passing the
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right configuration options to Salt when not using the script is tricky: the
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plan here is to simplify this by having Kubernetes take on more node
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configuration, and even potentially remove Salt altogether.
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### Manual infrastructure creation
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While this work is not yet complete, advanced users might choose to manually
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certain AWS objects while still making use of the kube-up script (to configure
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create certain AWS objects while still making use of the kube-up script (to configure
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Salt, for example). These objects can currently be manually created:
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* Set the `AWS_S3_BUCKET` environment variable to use an existing S3 bucket.
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