High availability configuration creates a replica of your primary master.
The primary master is your Puppet master or, if your installation includes compile masters, your master of masters. The replica node is called the primary master replica. You may only have one provisioned replica at a time.
There are two main advantages to enabling high availability:
If your primary master fails, the replica takes over, continuing to perform critical operations.
If your primary master can’t be repaired, you can promote the replica to master. Promotion establishes the replica as the new, permanent master.
High availability architecture
The primary master replica is not an exact copy of the primary master. Rather, the replica duplicates specific infrastructure components and services. Hiera data and other custom configurations are not replicated.
Replication may be read-write, meaning that data can be written to the service or component on either the master or the replica, and the data is synced to both nodes. Alternatively, replication may be read-only, where data is written only to the master and synced to the replica. Some components and services, like Puppet Server and the console service UI, are not replicated because they contain no native data.
Some components and services are activated immediately when you enable a replica; others aren't active until you promote a replica. After you provision and enable a replica, it serves as a compile master, redirecting PuppetDB and cert requests to the primary master.
|Component or service||Type of replication||Activated when replica is...|
|File sync client||read-only||enabled|
|Node classifier service||read-only||enabled|
|Console service UI||none||promoted|
In a monolithic installation, when a Puppet run fails over, agents communicate with the replica instead of the master. In a monolithic installation with compile masters, agents communicate with load balancers or compile masters, which communicate with the master or replica.
What happens during failovers
Failover occurs when the replica takes over services usually performed by the master.
Failover is automatic — you don’t have to take action to activate the replica. With high availability enabled, Puppet runs are directed first to the master. If the primary master is either fully or partially unreachable, runs are directed to the replica.
In partial failovers, Puppet runs may use the server, node classifier, or PuppetDB on the replica if those services aren’t reachable on the master. For example, if the master’s node classifier fails, but its Puppet Server is still running, agent runs use the Puppet Server on the master but fail over to the replica’s node classifier.
What works during failovers:
- Scheduled Puppet runs
- Catalog compilation
- Viewing classification data using the node classifier API
- Reporting and queries based on PuppetDB data
What doesn’t work during failovers:
- Deploying new Puppet code
- Editing node classifier data
- Using the console
- Certificate functionality, including provisioning new agents, revoking certificates, or running the
- Most CLI tools
- Application orchestration
System and software requirements
Your Puppet infrastructure must meet specific requirements in order to configure high availability.
|Operating system||All supported PE master platforms.|
|Firewall||Both the master and the replica must comply with these port requirements: |
Classification changes in high availability installations
When you provision and enable a replica, the system makes a number of classification changes in order to manage high availability without affecting existing configuration.
These preconfigured node groups are added in high availability installations:
|Node group||Matching nodes||Inherits from|
|PE HA Master||primary master||PE Master node group|
|PE HA Replica||primary master replicas||PE Infrastructure node group|
|Specifies the list of servers that agents contact, in order.||
PE Infrastructure Agent
In monolithic installations with compile masters, agents must be configured to communicate with the load balancers or compile masters.
Important: Setting agents to communicate directly with the replica in order to use the replica as a compile master is not a supported configuration.
|Sets replication type and direction on masters and replicas.||
PE Master (
HA Master (
HA Replica (
|System parameter. Don’t modify.|
|Tracks replica nodes that are failover ready.||PE Infrastructure||
System parameter. Don't modify.
Updated when you enable a replica.
|Specifies the list of Puppet Communications Protocol brokers that Puppet Execution Protocol agents contact, in order.||
PE Infrastructure Agent
Load balancer timeout in high availability installations
High availability configuration uses timeouts to determine when to fail over to the replica. If the load balancer timeout is shorter than the server and agent timeout, connections from agents might be terminated during failover.
To avoid timeouts, set the timeout option for load balancers to four minutes or longer. This duration allows compile masters enough time for required queries to PuppetDB and the node classifier service. You can set the load balancer timeout option using parameters in the haproxy or f5 modules.