c12s-kubespray/docs/ansible.md

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# Ansible variables
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## Inventory
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The inventory is composed of 3 groups:
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* **kube_node** : list of kubernetes nodes where the pods will run.
* **kube_control_plane** : list of servers where kubernetes control plane components (apiserver, scheduler, controller) will run.
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* **etcd**: list of servers to compose the etcd server. You should have at least 3 servers for failover purpose.
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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:
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```ShellSession
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 control-plane and node, the server must be defined
on both groups _kube_control_plane_ and _kube_node_. If you want a standalone and
unschedulable control plane, the server must be defined only in the _kube_control_plane_ and
not _kube_node_.
There are also two special groups:
* **calico_rr** : explained for [advanced Calico networking cases](calico.md)
* **bastion** : configure a bastion host if your nodes are not directly reachable
Below is a complete inventory example:
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```ini
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## Configure 'ip' variable to bind kubernetes services on a
## different ip than the default iface
node1 ansible_host=95.54.0.12 ip=10.3.0.1
node2 ansible_host=95.54.0.13 ip=10.3.0.2
node3 ansible_host=95.54.0.14 ip=10.3.0.3
node4 ansible_host=95.54.0.15 ip=10.3.0.4
node5 ansible_host=95.54.0.16 ip=10.3.0.5
node6 ansible_host=95.54.0.17 ip=10.3.0.6
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[kube_control_plane]
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node1
node2
[etcd]
node1
node2
node3
[kube_node]
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node2
node3
node4
node5
node6
[k8s_cluster:children]
kube_node
kube_control_plane
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```
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## Group vars and overriding variables precedence
The group variables to control main deployment options are located in the directory ``inventory/sample/group_vars``.
Optional variables are located in the `inventory/sample/group_vars/all.yml`.
Mandatory variables that are common for at least one role (or a node group) can be found in the
`inventory/sample/group_vars/k8s_cluster.yml`.
There are also role vars for docker, kubernetes preinstall and control plane roles.
According to the [ansible docs](https://docs.ansible.com/ansible/latest/playbooks_variables.html#variable-precedence-where-should-i-put-a-variable),
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those cannot be overridden from the group vars. In order to override, one should use
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the `-e` runtime flags (most simple way) or other layers described in the docs.
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Kubespray uses only a few layers to override things (or expect them to
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be overridden for roles):
Layer | Comment
------|--------
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**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
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playbook group_vars | Unused
playbook host_vars | Unused
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**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
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set_facts | Kubespray overrides those, for some places
**role and include vars** | Provides bad UX to override things! Use extra vars to enforce
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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``
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## Ansible tags
The following tags are defined in playbooks:
| Tag name | Used for
|--------------------------|---------
| apps | K8s apps definitions
| azure | Cloud-provider Azure
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| 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
| 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
| k8s-pre-upgrade | Upgrading K8s cluster
| k8s-secrets | Configuring K8s certs/keys
| 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
| ingress_alb | AWS ALB Ingress Controller
| ambassador | Ambassador Ingress Controller
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.
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## Example commands
Example command to filter and apply only DNS configuration tasks and skip
everything else related to host OS configuration and downloading images of containers:
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```ShellSession
ansible-playbook -i inventory/sample/hosts.ini cluster.yml --tags preinstall,facts --skip-tags=download,bootstrap-os
```
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And this play only removes the K8s cluster DNS resolver IP from hosts' /etc/resolv.conf files:
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```ShellSession
ansible-playbook -i inventory/sample/hosts.ini -e dns_mode='none' cluster.yml --tags resolvconf
```
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And this prepares all container images locally (at the ansible runner node) without installing
or upgrading related stuff or trying to upload container to K8s cluster nodes:
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```ShellSession
ansible-playbook -i inventory/sample/hosts.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.
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## Bastion host
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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.
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```ShellSession
[bastion]
bastion ansible_host=x.x.x.x
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```
For more information about Ansible and bastion hosts, read
[Running Ansible Through an SSH Bastion Host](https://blog.scottlowe.org/2015/12/24/running-ansible-through-ssh-bastion-host/)
## Mitogen
You can use [mitogen](mitogen.md) to speed up kubespray.