Docker Swarm

What Docker Swarm is

Docker Swarm is a cluster management feature built into Docker Engine for running workloads across multiple Docker daemons in production. It is managed through the Docker CLI and needs no additional orchestration software. Managers use a declarative model to maintain the requested service state, including replica counts, networks, storage resources, and exposed ports. Services can be replicated or run globally, with one task on every node. Swarm provides overlay networking between daemons, an ingress network for load balancing, and service discovery through DNS names, virtual IPs, or DNS round-robin. It supports incremental service updates and rollback to a previous version. Nodes authenticate and encrypt communications with mutual TLS, with TLS 1.2 as the minimum. Application data on overlay networks is not encrypted by default; enabling overlay encryption with IPsec can impose a non-negligible performance penalty. Nodes also require TCP/UDP port 7946 for network discovery and UDP port 4789 by default for overlay traffic. Docker recommends at most seven manager nodes and /24 overlay network blocks, which limit a network to 256 IP addresses.