Integrations

Clustershell

ClusterShell is a scalable cluster administration Python framework, designed to execute commands on many cluster nodes in parallel. ClusterShell supports the possibility to define groups of nodes. These groups can be extracted from external sources.

This section illustrates how to make ClusterShell extracts groups from RacksDB and tags associated to nodes with a simple example. In this example, let’s consider a cluster infrastructure named atlas.

Create file /etc/clustershell/groups.conf.d/racksdb.conf with this content:

[racksdb]
map:     racksdb nodes --infrastructure atlas --tags $GROUP --list
all:     racksdb nodes --infrastructure atlas --list
list:    racksdb tags --infrastructure atlas --on-nodes
reverse: racksdb tags --node $NODE

With this simple configuration, ClusterShell can extract groups and nodes from RacksDB. For example, with nodeset command:

  • Get the list of groups:

    $ nodeset -s racksdb -l
@racksdb:admin
@racksdb:compute
@racksdb:login

  • Get all nodes in compute group (ie. associated to compute tag in database):

    $ nodeset -f @racksdb:compute
atcn[1-2]

  • Get all nodes in this cluster:

    $ nodeset -f -s racksdb -a
atadmin,atcn[1-2],atlogin

ClusterShell can execute commands on nodes from these groups with clush:

# clush -bw @racksdb:compute uname
---------------
atcn[1-2] (2)
---------------
Linux

This way, ClusterShell groups are always synchronized with tags and content of RacksDB database. when RacksDB database is updated, changes are automatically reflected in ClusterShell.

More than one infrastructure?

If you need to extract groups from multiple infrastructures in RacksDB, a simple approach if to use ClusterShell multiple sources sections feature and $GROUP variable. For example, in /etc/clustershell/groups.conf.d/racksdb.conf:

[trinity,atlas]
map:     racksdb nodes --infrastructure $SOURCE --tags $GROUP --list
all:     racksdb nodes --infrastructure $SOURCE --list
list:    racksdb tags --infrastructure $SOURCE --on-nodes
reverse: racksdb tags --node $NODE

This way, RacksDB commands are executed for multiple infrastructures:

$ nodeset -f @trinity:compute
tricn[1-4]
$ nodeset -f @atlas:compute
atcn[1-2]

Another yet more generic approach to split the group source with shell:

[racksdb]
map:     GRP=$GROUP; racksdb nodes --infrastructure ${GRP%:*} --tags ${GRP#*:} --list
all:     racksdb nodes --list
reverse: racksdb tags --node $NODE

This way, infrastructures names are not mentioned in ClusterShell configuration file and all infrastructures defined in RacksDB can be requested:

$ nodeset -f @racksdb:trinity:compute
tricn[1-4]
$ nodeset -f @racksdb:atlas:compute
atcn[1-2]