Docker

By default, containers inherit DNS configuration from the Docker daemon. When you need to override that, three directives give you full control: dns:, dns_search:, and dns_opt:. Setting custom DNS servers dns: overrides which resolvers the container queries: services: app: image: myapp dns: - 1.1.1.1 - 8.8.8.8 The container now uses Cloudflare and Google DNS instead of whatever the host provides. Useful when: The host DNS is slow or unreliable for your use case You need a specific public DNS for content filtering (Pi-hole, NextDNS) A development environment must reach internal services through a corporate DNS server Search domains dns_search: adds search domains so short names resolve against them: ...

Need to grab a log file out of a container? Push a quick config change for a one-off test? Don’t redeploy with a bind mount, just use docker compose cp. Basic usage The syntax mirrors docker cp but resolves service names instead of container IDs: # Copy from container to host docker compose cp <service>:<container-path> <host-path> # Copy from host to container docker compose cp <host-path> <service>:<container-path> The direction is determined by which side has the service: prefix. ...

CPU and memory limits (Tip #16) cover the obvious resources. Two more options solve specific problems: ulimits for kernel limits and shm_size for shared memory. ulimits: kernel resource limits ulimits controls per-container limits the Linux kernel enforces: open file descriptors, processes, locked memory, and others. services: api: image: myapi ulimits: nofile: soft: 65536 hard: 65536 nproc: 4096 soft is the default, hard is the maximum the process can raise itself to. For most simple cases, set them equal. ...

By default, services in Compose are reachable by their service name. With aliases, you can give a service additional hostnames on a network, no extra DNS config required. Basic usage Add aliases under the network attachment: services: primary: image: postgres networks: app-net: aliases: - db - database - postgres-primary networks: app-net: From any other container on app-net, you can reach the service as primary, db, database, or postgres-primary. All four hostnames resolve to the same container. ...

Not everything in your stack is a container. Managed databases, SaaS APIs, VPN tunnels, Kubernetes intercepts, all sit outside Docker but still need to be wired into your local environment. Compose 2.36 introduced provider services to declare and manage these alongside your containers. The syntax A provider service replaces image: with a provider: block: services: api: image: my-api:latest tunnel: provider: type: telepresence options: namespace: avatars service: api port: 5732:api-80 Two parts: ...