Hardware Requirements
Resources (RAM, CPU, etc.)
Nomad servers may need to be run on large machine instances. We suggest having between 4-8+ cores, 16-32 GB+ of memory, 40-80 GB+ of fast disk and significant network bandwidth. The core count and network recommendations are to ensure high throughput as Nomad heavily relies on network communication and as the Servers are managing all the nodes in the region and performing scheduling. The memory and disk requirements are due to the fact that Nomad stores all state in memory and will store two snapshots of this data onto disk, which causes high IO in busy clusters with lots of writes. Thus disk should be at least 2 times the memory available to the server when deploying a high load cluster. When running on AWS prefer NVME or Provisioned IOPS SSD storage for data dir.
These recommendations are guidelines and operators should always monitor the resource usage of Nomad to determine if the machines are under or over-sized.
Nomad clients support reserving resources on the node that should not be used by Nomad. This should be used to target a specific resource utilization per node and to reserve resources for applications running outside of Nomad's supervision such as Consul and the operating system itself.
Please see the reservation configuration for more detail.
Network Topology
Nomad servers are expected to have sub 10 millisecond network latencies between each other to ensure liveness and high throughput scheduling. Nomad servers can be spread across multiple datacenters if they have low latency connections between them to achieve high availability.
For example, on AWS every region comprises of multiple zones which have very low latency links between them, so every zone can be modeled as a Nomad datacenter and every Zone can have a single Nomad server which could be connected to form a quorum and a region.
Nomad servers uses Raft for state replication and Raft being highly consistent needs a quorum of servers to function, therefore we recommend running an odd number of Nomad servers in a region. Usually running 3-5 servers in a region is recommended. The cluster can withstand a failure of one server in a cluster of three servers and two failures in a cluster of five servers. Adding more servers to the quorum adds more time to replicate state and hence throughput decreases so we don't recommend having more than seven servers in a region.
Nomad clients do not have the same latency requirements as servers since they are not participating in Raft. Thus clients can have 100+ millisecond latency to their servers. This allows having a set of Nomad servers that service clients that can be spread geographically over a continent or even the world in the case of having a single "global" region and many datacenter.
Ports Used
Nomad requires 3 different ports to work properly on servers and 2 on clients, some on TCP, UDP, or both protocols. Below we document the requirements for each port.
HTTP API (Default 4646). This is used by clients and servers to serve the HTTP API. TCP only.
RPC (Default 4647). This is used for internal RPC communication between client agents and servers, and for inter-server traffic. TCP only.
Serf WAN (Default 4648). This is used by servers to gossip both over the LAN and WAN to other servers. It isn't required that Nomad clients can reach this address. TCP and UDP.
When tasks ask for dynamic ports, they are allocated out of the port range between 20,000 and 32,000. This is well under the ephemeral port range suggested by the IANA. If your operating system's default ephemeral port range overlaps with Nomad's dynamic port range, you should tune the OS to avoid this overlap.
On Linux this can be checked and set as follows:
Bridge Networking and iptables
Nomad's task group networks and Consul Connect integration use bridge networking and iptables to send traffic between containers. The Linux kernel bridge module has three "tunables" that control whether traffic crossing the bridge are processed by iptables. Some operating systems (RedHat, CentOS, and Fedora in particular) configure these tunables to optimize for VM workloads where iptables rules might not be correctly configured for guest traffic.
These tunables can be set to allow iptables processing for the bridge network as follows:
To preserve these settings on startup of a client node, add a file including the following to /etc/sysctl.d/ or remove the file your Linux distribution puts in that directory.