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c12s-kubespray/docs/ansible.md
Bogdan Dobrelya a15d626771 Preconfigure DNS stack and docker early 
In order to enable offline/intranet installation cases:
* Move DNS/resolvconf configuration to preinstall role. Remove
  skip_dnsmasq_k8s var as not needed anymore.

* Preconfigure DNS stack early, which may be the case when downloading
  artifacts from intranet repositories. Do not configure
  K8s DNS resolvers for hosts /etc/resolv.conf yet early (as they may be
  not existing).

* Reconfigure K8s DNS resolvers for hosts only after kubedns/dnsmasq
  was set up and before K8s apps to be created.

* Move docker install task to early stage as well and unbind it from the
  etcd role's specific install path. Fix external flannel dependency on
  docker role handlers. Also fix the docker restart handlers' steps
  ordering to match the expected sequence (the socket then the service).

* Add default resolver fact, which is
  the cloud provider specific and remove hardcoded GCE resolver.

* Reduce default ndots for hosts /etc/resolv.conf to 2. Multiple search
  domains combined with high ndots values lead to poor performance of
  DNS stack and make ansible workers to fail very often with the
  "Timeout (12s) waiting for privilege escalation prompt:" error.

* Update docs.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>
2016-12-09 17:30:55 +01:00

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Ansible variables

Inventory

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. Note: 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
  • etcd: list of server to compose the etcd server. you should have at least 3 servers for failover purposes.

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
etcd

Group vars

The main variables to change are located in the directory inventory/group_vars/all.yml.

Ansible tags

The following tags are defined in playbooks:

Tag name Used for
apps K8s apps definitions
azure Cloud-provider Azure
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
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 self-hosted kube-apiserver
kube-controller-manager Configuring self-hosted kube-controller-manager
kubectl Installing kubectl and bash completion
kubelet Configuring kubelet service
kube-proxy Configuring self-hosted kube-proxy
kube-scheduler Configuring self-hosted kube-scheduler
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
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 dns_server='' cluster.yml --tags resolvconf

Note: use --tags and --skip-tags wise and only if you're 100% sure what you're doing.