Ansible Roles: Mesosphere DC/OS

A set of Ansible Roles that manage a DC/OS cluster lifecycle on RedHat/CentOS Linux.

Requirements

To make best use of these roles, your nodes should resemble the Mesosphere recommended way of setting up infrastructure. Depending on your setup, it is expected to deploy to:

• One or more master node ('masters')
• One bootstrap node ('bootstraps')
• Zero or more agent nodes, used for public facing services ('agents_public')
• One or more agent nodes, not used for public facing services ('agents_private')

An example inventory file is provided as shown here:

[bootstraps]
bootstrap1-dcos112s.example.com

[masters]
master1-dcos112s.example.com
master2-dcos112s.example.com
master3-dcos112s.example.com

[agents_private]
agent1-dcos112s.example.com
remoteagent1-dcos112s.example.com

[agents_public]
publicagent1-dcos112s.example.com

[agents:children]
agents_private
agents_public

[common:children]
bootstraps
masters
agents
agents_public

Role Variables

The Mesosphere DC/OS Ansible roles make use of two sets of variables:

1. A set of per-node type group_var's
2. A multi-level dictionary called dcos, that should be available to all nodes

Per group vars

[bootstraps:vars]
node_type=bootstrap

[masters:vars]
node_type=master
dcos_legacy_node_type_name=master

[agents_private:vars]
node_type=agent
dcos_legacy_node_type_name=slave

[agents_public:vars]
node_type=agent_public
dcos_legacy_node_type_name=slave_public

Global vars

dcos:
  download: "https://downloads.dcos.io/dcos/stable/1.13.4/dcos_generate_config.sh"
  download_checksum: "sha256:a3d295de33ad55b10f5dc66c9594d9175a40f5aaec7734d664493968a9f751fd"
  version: "1.13.4"
  enterprise_dcos: false
  selinux_mode: enforcing

  config:
    cluster_name: "examplecluster"
    security: strict
    bootstrap_url: http://int-bootstrap1-examplecluster.example.com:8080
    exhibitor_storage_backend: static
    master_discovery: static
    master_list:
      - 172.31.42.1

Cluster wide variables

Name	Required?	Description
download	REQUIRED	(https) URL to download the Mesosphere DC/OS install from
download_checksum	no	Checksum to check the download against. It should start with the method being used. E.g. "sha256:"
version	REQUIRED	Version string that reflects the version that the installer (given by download) installs. Can be collected by running dcos_generate_config.sh --version.
version_to_upgrade_from	for upgrades	Version string of Mesosphere DC/OS the upgrade procedure expectes to upgrade FROM. A per-version upgrade script will be generated on the bootstrap machine, each cluster node downloads the proper upgrade for its currenly running DC/OS version.
image_commit	no	Can be used to force same version / same config upgrades. Mostly useful for deploying/upgrading non-released versions, e.g. 1.12-dev. This parameter takes precedence over version.
enterprise_dcos	REQUIRED	Specifies if the installer (given by download) installs an 'open' or 'enterprise' version of Mesosphere DC/OS. This is required as there are additional post-upgrade checks for enterprise-only components.
selinux_mode	REQUIRED	Indicates the cluster nodes operating sytems SELinux mode. Mesosphere DC/OS supports running in enforcing mode starting with 1.12. Older versions require permissive.
config	yes	Yaml structure that represents a valid Mesosphere DC/OS config.yml, see below.

DC/OS config.yml parameters

Please see the official Mesosphere DC/OS configuration reference for a full list of possible parameters. There are a few parameters that are used by these roles outside the DC/OS config.yml, specifically:

• bootstrap_url: Should point to http://your bootstrap node:8080. Will be used internally and conviniently overwritten for the installer/upgrader to point to a version specific sub-directory.
• ip_detect_contents: Is used to determine a user-supplied IP detection script. Overwrites the build-in enviroment detection and usage of a generic AWS and/or on premise script. Official Mesosphere DC/OS ip-detect reference
• ip_detect_public_contents: Is used to determine a user-supplied public IP detection script. Overwrites the build-in enviroment detection and usage of a generic AWS and/or on premise script. Official Mesosphere DC/OS ip-detect reference
• fault_domain_detect_contents: Is used to determine a user-supplied fault domain detection script. Overwrites the build-in enviroment detection and usage of a generic AWS and/or on premise script.

Ansible dictionary merge behavior caveat

Due to the nested structure of the dcos configuration, it might be required to set Ansible to 'merge' instead of 'replace', when combining config from multiple places.

Example

# ansible.cfg
hash_behaviour = merge

Safeguard during interactive use: dcos_cluster_name_confirmed

When invoking these roles interactively (for example from the operator's machine), the DCOS.bootstrap role will require a manual confirmation of the cluster to run against. This is a safeguarding mechanism to avoid unintentional upgrade or config changes. In non-interactive plays, a variable can be set to skip this step, e.g.:

ansible-playbook -e 'dcos_cluster_name_confirmed=True' dcos.yml

Example playbook

Mesosphere DC/OS is a complex system, spanning multiple nodes to form a full multi-node cluster. There are some constraints in making a playbook use the provided roles:

1. Order of groups to run their respective roles on (e.g. bootstrap node first, then masters, then agents)
2. Concurrency for upgrades (e.g. serial: 1 for master nodes)

The provided dcos.yml playbook can be used as-is for installing and upgrading Mesosphere DC/OS.

Tested OS and Mesosphere DC/OS versions

• CentOS 7, RHEL 7
• DC/OS 1.12, both open as well as enterprise version

License

Apache 2.0

Author Information

This role was created by team SRE @ Mesosphere and others in 2018, based on multiple internal tools and non-public Ansible roles that have been developed internally over the years.