no-host-port-format
disallow “host:port” entries in “forwardPorts” and “portsAttributes”, which GitHub Codespaces does not support
Why
The “host:port” form forwards a port from another container in a Docker Compose project (e.g. “db:5432”) rather than from the primary one. Codespaces documents that it does not support that variation of either property, so the entry is ignored there and the port is not forwarded. A bare port number, which refers to the primary container, works everywhere.
Bad
{
"image": "mcr.microsoft.com/devcontainers/base:ubuntu",
"forwardPorts": ["db:5432"]
}
Good
{
"image": "mcr.microsoft.com/devcontainers/base:ubuntu",
"forwardPorts": [5432]
}