Raj Chaudhuri
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98 lines
3.5 KiB
Markdown
98 lines
3.5 KiB
Markdown
---
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title: Uniform Dynamic Clusters
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menu_order: 50
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search_type: Documentation
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---
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A uniform dynamic cluster has the following characteristics:
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* Recovers automatically after reboots and partitions.
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* Identical configuration for all of its peers.
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* Initial cluster peers can make progress from the outset even if
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bootstrapping occurs under conditions of partition.
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* Once an initial cluster has been bootstrapped, arbitrary numbers of
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new peers can be added in parallel without coordination. This makes
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it ideally suited for use with convergent provisioning tools that
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operate across multiple hosts in an asynchronous fashion.
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## Bootstrapping
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On each initial peer N, at boot, via
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[systemd]({{ '/install/systemd' | relative_url }}):
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hostN$ weave launch --no-restart --name ::N --ipalloc-init seed=$SEED $PEERS
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Where,
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* `$SEED` is a comma separated list of the _names_ of the initial
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peers, for example, `::1,::2,::3` and,
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* `$PEERS` is obtained from `/etc/sysconfig/weave` as described in the linked systemd
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documentation, and includes the complete set of initial peer
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_addresses_.
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For example, if you have three initial peers you would specify the
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following:
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host1$ weave launch --no-restart --name ::1 --ipalloc-init seed=$SEED $PEERS
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host2$ weave launch --no-restart --name ::2 --ipalloc-init seed=$SEED $PEERS
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host3$ weave launch --no-restart --name ::3 --ipalloc-init seed=$SEED $PEERS
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Where
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SEED="::1,::2,::3"
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PEERS="host1 host2 host3"
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## Adding a Peer
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On each new peer, at boot, via
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[systemd]({{ '/install/systemd' | relative_url }}):
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hostN$ weave launch --no-restart --name ::N --ipalloc-init seed=$SEED $PEERS
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Where,
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* `--no-restart` disables the Docker restart policy, since this will be
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handled by systemd.
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* `--name` specifies a unique name for this new peer.
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* `--ipalloc-init seed` specifies the names of only those peers that were
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involved in the initial cluster bootstrap - even if they have been
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subsequently removed from the cluster. You can view this as a kind
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of 'cluster identity',where peers may only interoperate in the same
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cluster if they share the same seed.
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* `$PEERS` is obtained from `/etc/sysconfig/weave` as described in the
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linked systemd documentation. For convenience, this may contain the
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address of the peer that is being launched, so that you don't have
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to compute separate lists of 'other' peers tailored to each peer -
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just supply the same complete list of peer addresses to every peer.
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Note that unlike [Interactive]({{ '/operational-guide/interactive' | relative_url }})
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and [Uniform Fixed Cluster]({{ '/operational-guide/uniform-fixed-cluster' | relative_url }}) deployments
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there is no `weave prime` step. You can add as many new peers in
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parallel as you like, even under conditions of partition, and they
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will all (eventually) join safely. This is ideal for use in
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conjunction with asynchronous provisioning systems such as puppet or
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chef.
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For maximum robustness, you should distribute an updated
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`/etc/sysconfig/weave` file including the new peer to all existing
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peers.
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### Removing a Peer
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On the peer to be removed:
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weave reset
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You may remove a seed peer, as long as there is at least one other
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seed peer left in the network.
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Then, distribute an updated `/etc/sysconfig/weave` to the remaining
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peers, omitting the removed peer from `$PEERS`.
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On each remaining peer:
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weave forget <removed peer>
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This step is not mandatory, but it will eliminate log noise and
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spurious network traffic by stopping reconnection attempts.
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