server Stanza

Placement	`server`

The server stanza configures the Nomad agent to operate in server mode to participate in scheduling decisions, register with service discovery, handle join failures, and more.

server {
  enabled          = true
  bootstrap_expect = 3
  server_join {
    retry_join = [ "1.1.1.1", "2.2.2.2" ]
    retry_max = 3
    retry_interval = "15s"
  }
}

`server` Parameters

authoritative_region (string: "") - Specifies the authoritative region, which provides a single source of truth for global configurations such as ACL Policies and global ACL tokens. Non-authoritative regions will replicate from the authoritative to act as a mirror. By default, the local region is assumed to be authoritative.
bootstrap_expect (int: required) - Specifies the number of server nodes to wait for before bootstrapping. It is most common to use the odd-numbered integers 3 or 5 for this value, depending on the cluster size. A value of 1 does not provide any fault tolerance and is not recommended for production use cases.
data_dir (string: "[data_dir]/server") - Specifies the directory to use - for server-specific data, including the replicated log. By default, this is - the top-level data_dir suffixed with "server", like "/opt/nomad/server". This must be an absolute path.
enabled (bool: false) - Specifies if this agent should run in server mode. All other server options depend on this value being set.
enabled_schedulers (array<string>: [all]) - Specifies which sub-schedulers this server will handle. This can be used to restrict the evaluations that worker threads will dequeue for processing.
enable_event_broker (bool: true) - Specifies if this server will generate events for its event stream.
encrypt (string: "") - Specifies the secret key to use for encryption of Nomad server's gossip network traffic. This key must be 32 bytes that are RFC4648 "URL and filename safe" base64-encoded. You can generate an appropriately-formatted key with the nomad operator keygen command. The provided key is automatically persisted to the data directory and loaded automatically whenever the agent is restarted. This means that to encrypt Nomad server's gossip protocol, this option only needs to be provided once on each agent's initial startup sequence. If it is provided after Nomad has been initialized with an encryption key, then the provided key is ignored and a warning will be displayed. See the encryption documentation for more details on this option and its impact on the cluster.
event_buffer_size (int: 100) - Specifies the number of events generated by the server to be held in memory. Increasing this value enables new subscribers to have a larger look back window when initially subscribing. Decreasing will lower the amount of memory used for the event buffer.
node_gc_threshold (string: "24h") - Specifies how long a node must be in a terminal state before it is garbage collected and purged from the system. This is specified using a label suffix like "30s" or "1h".
job_gc_interval (string: "5m") - Specifies the interval between the job garbage collections. Only jobs who have been terminal for at least job_gc_threshold will be collected. Lowering the interval will perform more frequent but smaller collections. Raising the interval will perform collections less frequently but collect more jobs at a time. Reducing this interval is useful if there is a large throughput of tasks, leading to a large set of dead jobs. This is specified using a label suffix like "30s" or "3m". job_gc_interval was introduced in Nomad 0.10.0.
job_gc_threshold (string: "4h") - Specifies the minimum time a job must be in the terminal state before it is eligible for garbage collection. This is specified using a label suffix like "30s" or "1h".
eval_gc_threshold (string: "1h") - Specifies the minimum time an evaluation must be in the terminal state before it is eligible for garbage collection. This is specified using a label suffix like "30s" or "1h".
deployment_gc_threshold (string: "1h") - Specifies the minimum time a deployment must be in the terminal state before it is eligible for garbage collection. This is specified using a label suffix like "30s" or "1h".
csi_volume_claim_gc_threshold (string: "1h") - Specifies the minimum age of a CSI volume before it is eligible to have its claims garbage collected. This is specified using a label suffix like "30s" or "1h".
csi_plugin_gc_threshold (string: "1h") - Specifies the minimum age of a CSI plugin before it is eligible for garbage collection if not in use. This is specified using a label suffix like "30s" or "1h".
default_scheduler_config (scheduler_configuration: nil) - Specifies the initial default scheduler config when bootstrapping cluster. The parameter is ignored once the cluster is bootstrapped or value is updated through the API endpoint. See the example section for more details default_scheduler_config was introduced in Nomad 0.10.4.
heartbeat_grace (string: "10s") - Specifies the additional time given as a grace period beyond the heartbeat TTL of nodes to account for network and processing delays as well as clock skew. This is specified using a label suffix like "30s" or "1h".
min_heartbeat_ttl (string: "10s") - Specifies the minimum time between node heartbeats. This is used as a floor to prevent excessive updates. This is specified using a label suffix like "30s" or "1h". Lowering the minimum TTL is a tradeoff as it lowers failure detection time of nodes at the tradeoff of false positives and increased load on the leader.
max_heartbeats_per_second (float: 50.0) - Specifies the maximum target rate of heartbeats being processed per second. This allows the TTL to be increased to meet the target rate. Increasing the maximum heartbeats per second is a tradeoff as it lowers failure detection time of nodes at the tradeoff of false positives and increased load on the leader.
non_voting_server (bool: false) - (Enterprise-only) Specifies whether this server will act as a non-voting member of the cluster to help provide read scalability.
num_schedulers (int: [num-cores]) - Specifies the number of parallel scheduler threads to run. This can be as many as one per core, or 0 to disallow this server from making any scheduling decisions. This defaults to the number of CPU cores.
protocol_version (int: 1) - Specifies the Nomad protocol version to use when communicating with other Nomad servers. This value is typically not required as the agent internally knows the latest version, but may be useful in some upgrade scenarios.
raft_protocol (int: 2) - Specifies the Raft protocol version to use when communicating with other Nomad servers. This affects available Autopilot features and is typically not required as the agent internally knows the latest version, but may be useful in some upgrade scenarios.
raft_multiplier (int: 1) - An integer multiplier used by Nomad servers to scale key Raft timing parameters. Omitting this value or setting it to 0 uses default timing described below. Lower values are used to tighten timing and increase sensitivity while higher values relax timings and reduce sensitivity. Tuning this affects the time it takes Nomad to detect leader failures and to perform leader elections, at the expense of requiring more network and CPU resources for better performance. The maximum allowed value is 10.
By default, Nomad will use the highest-performance timing, currently equivalent to setting this to a value of 1. Increasing the timings makes leader election less likely during periods of networking issues or resource starvation. Since leader elections pause Nomad's normal work, it may be beneficial for slow or unreliable networks to wait longer before electing a new leader. The tradeoff when raising this value is that during network partitions or other events (server crash) where a leader is lost, Nomad will not elect a new leader for a longer period of time than the default. The nomad.nomad.leader.barrier and nomad.raft.leader.lastContact metrics are a good indicator of how often leader elections occur and raft latency.
redundancy_zone (string: "") - (Enterprise-only) Specifies the redundancy zone that this server will be a part of for Autopilot management. For more information, see the Autopilot Guide.
rejoin_after_leave (bool: false) - Specifies if Nomad will ignore a previous leave and attempt to rejoin the cluster when starting. By default, Nomad treats leave as a permanent intent and does not attempt to join the cluster again when starting. This flag allows the previous state to be used to rejoin the cluster.
server_join (server_join: nil) - Specifies how the Nomad server will connect to other Nomad servers. The retry_join fields may directly specify the server address or use go-discover syntax for auto-discovery. See the server_join documentation for more detail.
upgrade_version (string: "") - A custom version of the format X.Y.Z to use in place of the Nomad version when custom upgrades are enabled in Autopilot. For more information, see the Autopilot Guide.

Deprecated Parameters

retry_join (array<string>: []) - Specifies a list of server addresses to retry joining if the first attempt fails. This is similar to start_join, but only invokes if the initial join attempt fails. The list of addresses will be tried in the order specified, until one succeeds. After one succeeds, no further addresses will be contacted. This is useful for cases where we know the address will become available eventually. Use retry_join with an array as a replacement for start_join, do not use both options. See the server_join section for more information on the format of the string. This field is deprecated in favor of the server_join stanza.
retry_interval (string: "30s") - Specifies the time to wait between retry join attempts. This field is deprecated in favor of the server_join stanza.
retry_max (int: 0) - Specifies the maximum number of join attempts to be made before exiting with a return code of 1. By default, this is set to 0 which is interpreted as infinite retries. This field is deprecated in favor of the server_join stanza.
start_join (array<string>: []) - Specifies a list of server addresses to join on startup. If Nomad is unable to join with any of the specified addresses, agent startup will fail. See the server address format section for more information on the format of the string. This field is deprecated in favor of the server_join stanza.

`server` Examples

Common Setup

This example shows a common Nomad agent server configuration stanza. The two IP addresses could also be DNS, and should point to the other Nomad servers in the cluster

server {
  enabled          = true
  bootstrap_expect = 3

  server_join {
    retry_join     = [ "1.1.1.1", "2.2.2.2" ]
    retry_max      = 3
    retry_interval = "15s"
  }
}

Configuring Data Directory

This example shows configuring a custom data directory for the server data.

server {
  data_dir = "/opt/nomad/server"
}

Automatic Bootstrapping

The Nomad servers can automatically bootstrap if Consul is configured. For a more detailed explanation, please see the automatic Nomad bootstrapping documentation.

Restricting Schedulers

This example shows restricting the schedulers that are enabled as well as the maximum number of cores to utilize when participating in scheduling decisions:

server {
  enabled            = true
  enabled_schedulers = ["batch", "service"]
  num_schedulers     = 7
}

Bootstrapping with a Custom Scheduler Config

While bootstrapping a cluster, you can use the default_scheduler_config stanza to prime the cluster with a SchedulerConfig. The scheduler configuration determines which scheduling algorithm is configured— spread scheduling or binpacking—and which job types are eligible for preemption.

Warning: Once the cluster is bootstrapped, you must configure this using the update scheduler configuration API. This option is only consulted during bootstrap.

The structure matches the Update Scheduler Config API endpoint, which you should consult for canonical documentation. However, the attributes names must be adapted to HCL syntax by using snake case representations rather than camel case.

This example shows configuring spread scheduling and enabling preemption for all job-type schedulers.

server {
  default_scheduler_config {
    scheduler_algorithm = "spread"

    preemption_config {
      batch_scheduler_enabled   = true
      system_scheduler_enabled  = true
      service_scheduler_enabled = true
    }
  }
}