Introduction

The various tools for administering Pacemaker clusters (crm_mon, crm shell, cibadmin and friends, Python GUI, Hawk) can be used by the root user, or any user in the haclient group. By default, these users have full read/write access. Starting with Pacemaker version 1.1.5, flexible access control lists are introduced to provide different levels of administration to different users.

Prerequisites

  • Users are regular UNIX users, so the same user accounts must be present on all nodes in the cluster.

  • All user accounts must be in the haclient group.

  • Pacemaker 1.1.5 or newer must be installed on all cluster nodes.

  • The CIB must be configured to use the pacemaker-1.1 or 1.2 schema. This can be set by running: 

    cibadmin --modify --xml-text '<cib validate-with="pacemaker-1.1"/>'

  • The enable-acl option must be set. If ACLs are not explicitly enabled, the previous behaviour will be used (i.e. all users in the haclient group have full access): 

    crm configure property enable-acl=true

  • Once this is done, ACLs can be configured as described below.

  • Note that the root and hacluster users will always have full access.

  • If nonprivileged users will be using the crm shell and CLI tools (as opposed to only using Hawk or the Python GUI) they will need to have /usr/sbin added to their path.

Configuring ACLs

Access control lists consist of an ordered set of access rules. Each rule allows read or write access or denies access completely to a part of the CIB. Rules are typically combined to produce a specific role, then users may be assigned to that role. It is also possible to configure ACLs directly for individual users.

ACLs may be configured using the crm shell or the Python GUI. The shell syntax is documented here. Using the Python GUI should be reasonably straightforward once the concepts are understood.

Note that rules are applied from first to last with the first matching rule being used. This means specific write rules usually need to be listed before general read rules. Any permission not explicitly granted is denied by default, but note that write implies read, so there is no need to specicify both to allow full read/write access.

Minimum Required ACLs

In order for the various tools to work correctly, a certain minimum amount of data must be readable by the user invoking the tool. In general, the safest thing to do is simply allow all users and roles read access to the entire CIB.

Role Syntax

An ACL role is a set of rules which describe access rights to CIB. Rules consist of an access right read, write, or deny and a specification denoting part of the configuration to which the access right applies. The specification can be an XPath or a combination of tag and id references. If an attribute is appended, then the specification applies only to that attribute of the matching element.

Usage

    role <role-id> rule [rule ...]

    rule :: acl-right cib-spec [attribute:<attribute>]

    acl-right :: read | write | deny

    cib-spec :: xpath-spec | tag-ref-spec
    xpath-spec :: xpath:<xpath>
    tag-ref-spec :: tag:<tag> | ref:<id> | tag:<tag> ref:<id>

Example Role: Read-only Access

    role monitor \
        read xpath:"/cib"

This is a single rule which allows read-only access to the entire CIB. Users with this role will be able to view the status of the cluster, but not make any changes.

Example Role: “Operator” Access

    role operator \
        write xpath:"//crm_config//nvpair[@name='maintenance-mode']" \
        write xpath:"//op_defaults//nvpair[@name='record-pending']" \
        write xpath:"//nodes/node//nvpair[@name='standby']" \
        write xpath:"//resources//nvpair[@name='target-role']" \
        write xpath:"//resources//nvpair[@name='is-managed']" \
        write xpath:"//constraints/rsc_location" \
        read xpath:"/cib"

These rules specify that users with this role will be able to:

  1. Turn maintenance mode on or off

  2. Change whether pending operations are recorded

  3. Put any node on standby, and bring any node back online

  4. Start, stop, promote or demote any resource

  5. Tell the cluster to manage, or not manage any resource

  6. Migrate/move resources from node to note

  7. View the status of the cluster

Users with this role will not be able to reconfigure resources (change parameters, operations, etc.) or colocation or ordering constraints.

Example Role: Full Access

    role administrator \
        write xpath:"/cib"

This is a single rule which allows rull read-write access to the entirue CIB. Users with this role will have equivalent access to the root and hacluster users.

User Syntax

ACLs can be defined for individual users using the same syntax as for roles. Alternately, users can simply be assigned a given role. The latter is considered best practice.

Usage

    user <uid> {role:<role-ref>|rule [rule ...]}

    rule :: acl-right cib-spec [attribute:<attribute>]

    acl-right :: read | write | deny

    cib-spec :: xpath-spec | tag-ref-spec
    xpath-spec :: xpath:<xpath>
    tag-ref-spec :: tag:<tag> | ref:<id> | tag:<tag> ref:<id>

Example

    user alice role:monitor
    user bob role:operator

The above example assigns alice the monitor role and bob the operator role.

Advanced Usage

Because ACLs can refer to elements and attributes in the CIB in a very granular way, it is possible to configure very specific rules. A refinement of the “operator” role above would be to allow manipulation of only a specific resource, for example:

    role bigdb_admin \
        write xpath:"//primitive[@id='bigdb']/meta_attributes/nvpair[@name='target-role']" \
        write xpath:"//primitive[@id='bigdb']/meta_attributes/nvpair[@name='is-managed']" \
        write xpath:"//constraints/rsc_location[@rsc='bigdb']" \
        read ref:"bigdb" \
        read xpath:"//nodes/node" uname \
        read xpath:"//nodes/node" type \
        read xpath:"//crm_config/cluster_property_set" \
        read xpath:"/cib/status"

The first four rules are specific for the bigdb resource. They allow modifying the target-role and is-managed meta attributes which effectively enables users in this role to stop/start and manage/unmanage the resource. The constraints write access rule allows moving the resource around. Finally, the user is granted read access to the resource definition.

The bottom four rules are the absolute minimum read permissions necessary for proper operation of various Pacemaker tools, including crm_mon and the shell. This is fine for viewing cluster status, but there are some tools for which this will not be sufficient access (notably ptest), which is why it is generally recommened that read access be allowed to the entire CIB.