An autoscaling configuration begins with a fixed cluster:
- Configured as per the Uniform Fixed Cluster scenario.
- Hosted on reserved or protected instances to ensure long-term stability.
- Ideally sized at a minimum of three or five nodes (you can make your fixed cluster bigger to accommodate base load as required; a minimum is specified here in the interests of resilience only.)
Building on this foundation, arbitrary numbers of dynamic peers can be added or removed concurrently as desired, without requiring any changes to the configuration of the fixed cluster. As with the fixed cluster, dynamically added nodes recover automatically from reboots and partitions.
On the additional dynamic peer, at boot, via systemd or equivalent:
weave launch --no-restart --ipalloc-init=observer $PEERS
$PEERSmeans all peers in the fixed cluster, initial and subsequently added, which have not been explicitly removed. It should include fixed peers which are temporarily offline or stopped.
You do not have to keep track of and specify the addresses
of other dynamic peers in
$PEERS - they will discover and connect to
each other via the fixed cluster.
Note: The use of
--ipalloc-init=observerprevents dynamic peers from coming to a consensus on their own - this is important to stop a clique forming amongst a group of dynamically added peers if they become partitioned from the fixed cluster after having learned about each other via discovery.
On the dynamic peer to be removed:
If for any reason you cannot arrange for
weave reset to be run on
the peer before the underlying host is destroyed (for example when
using spot instances that can be destroyed without notice), you will
need an asynchronous process to reclaim lost IP address