The Kubernetes cluster can be configured using Salt.
The Salt scripts are shared across multiple hosting providers, so it's important to understand some background information prior to making a modification to ensure your changes do not break hosting Kubernetes across multiple environments. Depending on where you host your Kubernetes cluster, you may be using different operating systems and different networking configurations. As a result, it's important to understand some background information before making Salt changes in order to minimize introducing failures for other hosting providers.
The salt-master service runs on the kubernetes-master node.
The salt-minion service runs on the kubernetes-master node and each kubernetes-minion node in the cluster.
Each salt-minion service is configured to interact with the salt-master service hosted on the kubernetes-master via the master.conf file.
[root@kubernetes-master] $ cat /etc/salt/minion.d/master.conf
master: kubernetes-master
The salt-master is contacted by each salt-minion and depending upon the machine information presented, the salt-master will provision the machine as either a kubernetes-master or kubernetes-minion with all the required capabilities needed to run Kubernetes.
If you are running the Vagrant based environment, the salt-api service is running on the kubernetes-master. It is configured to enable the vagrant user to introspect the salt cluster in order to find out about machines in the Vagrant environment via a REST API.
Security is not enabled on the salt-master, and the salt-master is configured to auto-accept incoming requests from minions. It is not recommended to use this security configuration in production environments without deeper study. (In some environments this isn't as bad as it might sound if the salt master port isn't externally accessible and you trust everyone on your network.)
[root@kubernetes-master] $ cat /etc/salt/master.d/auto-accept.conf
open_mode: True
auto_accept: True
Each minion in the salt cluster has an associated configuration that instructs the salt-master how to provision the required resources on the machine.
An example file is presented below using the Vagrant based environment.
[root@kubernetes-master] $ cat /etc/salt/minion.d/grains.conf
grains:
master_ip: $MASTER_IP
etcd_servers: $MASTER_IP
cloud_provider: vagrant
roles:
- kubernetes-master
Each hosting environment has a slightly different grains.conf file that is used to build conditional logic where required in the Salt files.
The following enumerates the set of defined key/value pairs that are supported today. If you add new ones, please make sure to update this list.
| Key | Value |
|---|---|
cbr-cidr |
(Optional) The minion IP address range used for the docker container bridge. |
cloud |
(Optional) Which IaaS platform is used to host kubernetes, gce, azure |
cloud_provider |
(Optional) The cloud_provider used by apiserver: gce, azure, vagrant |
etcd_servers |
(Optional) Comma-delimited list of IP addresses the apiserver and kubelet use to reach etcd. Uses the IP of the first machine in the kubernetes_master role. |
hostnamef |
(Optional) The full host name of the machine, i.e. hostname -f |
master_ip |
(Optional) The IP address that the apiserver will bind against |
node_ip |
(Optional) The IP address to use to address this node |
minion_ip |
(Optional) Mapped to the kubelet hostname_override, K8S TODO - change this name |
network_mode |
(Optional) Networking model to use among nodes: openvswitch |
roles |
(Required) 1. kubernetes-master means this machine is the master in the kubernetes cluster. 2. kubernetes-pool means this machine is a kubernetes-minion. Depending on the role, the Salt scripts will provision different resources on the machine. |
These keys may be leveraged by the Salt sls files to branch behavior.
In addition, a cluster may be running a Debian based operating system or Red Hat based operating system (Centos, Fedora, RHEL, etc.). As a result, its important to sometimes distinguish behavior based on operating system using if branches like the following.
{% if grains['os_family'] == 'RedHat' %}
// something specific to a RedHat environment (Centos, Fedora, RHEL) where you may use yum, systemd, etc.
{% else %}
// something specific to Debian environment (apt-get, initd)
{% endif %}
- When configuring default arguments for processes, its best to avoid the use of EnvironmentFiles (Systemd in Red Hat environments) or init.d files (Debian distributions) to hold default values that should be common across operating system environments. This helps keep our Salt template files easy to understand for editors that may not be familiar with the particulars of each distribution.
Per pod IP configuration is provider specific, so when making networking changes, its important to sand-box these as all providers may not use the same mechanisms (iptables, openvswitch, etc.)
We should define a grains.conf key that captures more specifically what network configuration environment is being used to avoid future confusion across providers.