Developer tools · Docker run to Docker compose converter
Docker networking in Compose: bridge, host, and the default network
· Background
docker compose networking
Docker's networking model changed a lot between the early --link days and today's user-defined networks. This post explains the modes, what Compose creates automatically, and how --network flags convert.
The web container cannot find the database — the old docker run used --link, the new file has nothing
The web container cannot find the database — the old docker run used --link, the new file has nothing. Evidence: --link is consumed and warned as legacy rather than becoming YAML. Reproduce network attachment with disposable literals. Pair each source occurrence with network_mode networks links; reserve DNS and topology for destination review.
The networking incident also reveals that A separate networking incident boundary is that host none bridge private and container-prefixed values become network_mode. Evidence: host none bridge private and container-prefixed values become network_mode. This network attachment constraint is a stopping point. Inspect network_mode networks links without manufacturing behavior, then document a host check for DNS and topology.
The converter declares user-named networks external; it does not build a multi-service default network
The default bridge and user-defined bridges — why service names resolve only on the latter. Evidence: a single-service converter cannot construct project DNS relationships; The converter declares user-named networks external; it does not build a multi-service default network. Trace network attachment tokens into network_mode networks links. Separate ordered values from last-value fields; DNS and topology is outside collection.
A related networking mechanism boundary is that for this networking section keep the original for this networking section command and warnings for this networking section beside this candidate file. Evidence: the repository gives no broader runtime or historical proof. Use this network attachment fact to predict one member or scalar in network_mode networks links. Check warnings before deciding anything about DNS and topology.
Project-network DNS behavior is not generated or tested by this single-service converter
What Compose creates for you — a project network where every service has a DNS name. Evidence: a custom network becomes a service entry plus an external declaration; Project-network DNS behavior is not generated or tested by this single-service converter. Judge network attachment serialization from its model. Quoting in network_mode networks links protects types but gives no operational proof for DNS and topology.
The second networking serialization observation is keep for this networking section the original command for this networking section and warnings beside for this networking section this candidate file that networking serialization result separates represented for this networking section configuration from absent context for this networking section image metadata is outside the networking serialization transformation. This network attachment output separates settings from unavailable context. Keep network_mode networks links reviewable and check DNS and topology independently.
--network host and none — network_mode: host, its Linux-focused nature, and ports being ignored
--network host and none — network_mode: host, its Linux-focused nature, and ports being ignored. Stop at the network attachment exception instead of guessing. Any addition near network_mode networks links needs a deployment-specific reason tied to DNS and topology.
Another networking exception constraint is that A separate networking exception boundary is that overlay macvlan aliases and fixed addresses need manual work. Evidence: overlay macvlan aliases and fixed addresses need manual work. Keep the original network attachment command beside warnings. The comparison shows what network_mode networks links contains and which DNS and topology decision remains manual.
container:x is preserved as network_mode: container:x, not rewritten to service:x
--network container:x — network_mode: service:x in Compose and its uses for VPN sidecars. Evidence: container:x remains literal and is not rewritten to service:x; container:x is preserved as network_mode: container:x, not rewritten to service:x. Build the network attachment example from synthetic names. Make every network_mode networks links item traceable without exposing production DNS and topology details.
The same networking example sample demonstrates that for this networking section keep the original for this networking section command and warnings for this networking section beside this candidate file. The paired network attachment fact should be visible in network_mode networks links. Record that line and avoid assumptions about DNS and topology.
--link is warned as legacy and omitted instead of becoming a links key
--link — the legacy links: key, what it did, and why service names replace it. Evidence: no links key is produced and peers must be modeled manually; --link is warned as legacy and omitted instead of becoming a links key. Translate the network attachment consequence into one observable network_mode networks links difference. Docker owns the later DNS and topology verdict.
The networking consequence implementation also shows for this networking section keep the original for this networking section command and warnings beside for this networking section this candidate file that networking consequence fact defines what for this networking section the browser contributed for this networking section docker still owns the networking consequence runtime verdict the for this networking section operator still owns the networking consequence security policy the for this networking section repository still needs the networking consequence secret removed keep for this networking section those responsibilities separate when for this networking section describing the generated service. Split network attachment responsibilities: conversion writes network_mode networks links, the repository removes secrets, and operators validate DNS and topology.
What this does not cover — overlay networks, macvlan and IPv6 configuration
What this does not cover — overlay networks, macvlan and IPv6 configuration. Limit network attachment scope to network_mode networks links branches shown here. Neighboring forms and defaults cannot answer DNS and topology questions.
One more networking scope limit follows from A separate networking limit boundary is that a single-service converter cannot construct project DNS relationships. Evidence: a single-service converter cannot construct project DNS relationships. Treat this network attachment boundary as an exclusion. Prefer accurate network_mode networks links over guesses about DNS and topology.
Read warnings alongside network_mode and external network declarations
Takeaway: Compose networks are the modern --link — and converting a command with --network shows how the flag is represented in the service. Evidence: host mode warns that published ports have no runtime effect; Read warnings alongside network_mode and external network declarations. Audit network attachment as source option, model field, network_mode networks links line and warning. Remove secrets before checking DNS and topology.
Finally, the networking takeaway source confirms keep the original command for this networking section and warnings beside for this networking section this candidate file that networking takeaway conclusion improves auditability for this networking section without promising equivalence shell for this networking section parsing remains outside the networking takeaway guarantee. Close network attachment narrowly: network_mode networks links is a candidate; DNS and topology and shell equivalence are not guarantees.