The inventory is composed of 3 groups:
- kube-node : list of kubernetes nodes where the pods will run.
- kube-master : list of servers where kubernetes master components (apiserver, scheduler, controller) will run.
- etcd: list of servers to compose the etcd server. You should have at least 3 servers for failover purpose.
Note: do not modify the children of k8s-cluster, like putting the etcd group into the k8s-cluster, unless you are certain to do that and you have it fully contained in the latter:
k8s-cluster ⊂ etcd => kube-node ∩ etcd = etcd
When kube-node contains etcd, you define your etcd cluster to be as well schedulable for Kubernetes workloads. If you want it a standalone, make sure those groups do not intersect. If you want the server to act both as master and node, the server must be defined on both groups kube-master and kube-node. If you want a standalone and unschedulable master, the server must be defined only in the kube-master and not kube-node.
There are also two special groups:
- calico-rr : explained for advanced Calico networking cases
- bastion : configure a bastion host if your nodes are not directly reachable
Below is a complete inventory example:
## Configure 'ip' variable to bind kubernetes services on a
## different ip than the default iface
node1 ansible_ssh_host=95.54.0.12 ip=10.3.0.1
node2 ansible_ssh_host=95.54.0.13 ip=10.3.0.2
node3 ansible_ssh_host=95.54.0.14 ip=10.3.0.3
node4 ansible_ssh_host=95.54.0.15 ip=10.3.0.4
node5 ansible_ssh_host=95.54.0.16 ip=10.3.0.5
node6 ansible_ssh_host=95.54.0.17 ip=10.3.0.6
[kube-master]
node1
node2
[etcd]
node1
node2
node3
[kube-node]
node2
node3
node4
node5
node6
[k8s-cluster:children]
kube-node
kube-master
The group variables to control main deployment options are located in the directory inventory/group_vars.
Optional variables are located in the inventory/group_vars/all.yml.
Mandatory variables that are common for at least one role (or a node group) can be found in the
inventory/group_vars/k8s-cluster.yml.
There are also role vars for docker, rkt, kubernetes preinstall and master roles.
According to the ansible docs,
those cannot be overriden from the group vars. In order to override, one should use
the -e runtime flags (most simple way) or other layers described in the docs.
Kubespray uses only a few layers to override things (or expect them to be overriden for roles):
| Layer | Comment |
|---|---|
| role defaults | provides best UX to override things for Kubespray deployments |
| inventory vars | Unused |
| inventory group_vars | Expects users to use all.yml,k8s-cluster.yml etc. to override things |
| inventory host_vars | Unused |
| playbook group_vars | Unused |
| playbook host_vars | Unused |
| host facts | Kubespray overrides for internal roles' logic, like state flags |
| play vars | Unused |
| play vars_prompt | Unused |
| play vars_files | Unused |
| registered vars | Unused |
| set_facts | Kubespray overrides those, for some places |
| role and include vars | Provides bad UX to override things! Use extra vars to enforce |
| block vars (only for tasks in block) | Kubespray overrides for internal roles' logic |
| task vars (only for the task) | Unused for roles, but only for helper scripts |
| extra vars (always win precedence) | override with ansible-playbook -e @foo.yml |
The following tags are defined in playbooks:
| Tag name | Used for |
|---|---|
| apps | K8s apps definitions |
| azure | Cloud-provider Azure |
| bastion | Setup ssh config for bastion |
| bootstrap-os | Anything related to host OS configuration |
| calico | Network plugin Calico |
| canal | Network plugin Canal |
| cloud-provider | Cloud-provider related tasks |
| dnsmasq | Configuring DNS stack for hosts and K8s apps |
| docker | Configuring docker for hosts |
| download | Fetching container images to a delegate host |
| etcd | Configuring etcd cluster |
| etcd-pre-upgrade | Upgrading etcd cluster |
| etcd-secrets | Configuring etcd certs/keys |
| etchosts | Configuring /etc/hosts entries for hosts |
| facts | Gathering facts and misc check results |
| flannel | Network plugin flannel |
| gce | Cloud-provider GCP |
| hyperkube | Manipulations with K8s hyperkube image |
| k8s-pre-upgrade | Upgrading K8s cluster |
| k8s-secrets | Configuring K8s certs/keys |
| kpm | Installing K8s apps definitions with KPM |
| kube-apiserver | Configuring static pod kube-apiserver |
| kube-controller-manager | Configuring static pod kube-controller-manager |
| kubectl | Installing kubectl and bash completion |
| kubelet | Configuring kubelet service |
| kube-proxy | Configuring static pod kube-proxy |
| kube-scheduler | Configuring static pod kube-scheduler |
| localhost | Special steps for the localhost (ansible runner) |
| master | Configuring K8s master node role |
| netchecker | Installing netchecker K8s app |
| network | Configuring networking plugins for K8s |
| nginx | Configuring LB for kube-apiserver instances |
| node | Configuring K8s minion (compute) node role |
| openstack | Cloud-provider OpenStack |
| preinstall | Preliminary configuration steps |
| resolvconf | Configuring /etc/resolv.conf for hosts/apps |
| upgrade | Upgrading, f.e. container images/binaries |
| upload | Distributing images/binaries across hosts |
| weave | Network plugin Weave |
Note: Use the bash scripts/gen_tags.sh command to generate a list of all
tags found in the codebase. New tags will be listed with the empty "Used for"
field.
Example command to filter and apply only DNS configuration tasks and skip everything else related to host OS configuration and downloading images of containers:
ansible-playbook -i inventory/inventory.ini cluster.yml --tags preinstall,dnsmasq,facts --skip-tags=download,bootstrap-os
And this play only removes the K8s cluster DNS resolver IP from hosts' /etc/resolv.conf files:
ansible-playbook -i inventory/inventory.ini -e dnsmasq_dns_server='' cluster.yml --tags resolvconf
And this prepares all container images localy (at the ansible runner node) without installing or upgrading related stuff or trying to upload container to K8s cluster nodes:
ansible-playbook -i inventory/inventory.ini cluster.yml \
-e download_run_once=true -e download_localhost=true \
--tags download --skip-tags upload,upgrade
Note: use --tags and --skip-tags wise and only if you're 100% sure what you're doing.
If you prefer to not make your nodes publicly accessible (nodes with private IPs only), you can use a so called bastion host to connect to your nodes. To specify and use a bastion, simply add a line to your inventory, where you have to replace x.x.x.x with the public IP of the bastion host.
bastion ansible_ssh_host=x.x.x.x
For more information about Ansible and bastion hosts, read Running Ansible Through an SSH Bastion Host