Error: dial tcp: lookup postgres.railway.internal on xxx.xxx.xxx.xxx:zz: no such host

Question

The objective I am trying to achieve is to: **apply database migrations**.

I have followed the docs the best I can to achieve this. My attempt now is to try and run migrations before pre-deployment by including the steps in the `railpack.json` file like so:  
  
\`\`\`json

```json
{
    "$schema": "https://schema.railpack.com",
    "steps": {
        "install": {
            "commands": [
                "curl -fsSL https://github.com/amacneil/dbmate/releases/latest/download/dbmate-linux-amd64 -o /usr/local/bin/dbmate && chmod +x /usr/local/bin/dbmate"
            ]
        },
        "migrate": {
            "inputs": [{ "step": "install" }],
            "commands": [
                "dbmate --wait-timeout=10s up"
            ]
        }
    },
    "deploy": {
      "startCommand": "hypercorn main:app --bind \"[::]:$PORT\""
    }
}
```

The migration cli `dbmate` reads the env variable `DATABASE_URL` which I set it to reference the postgres service's own private `DATABASE_URL`. However, I get an error when it runs. The error says:

```
dbmate --wait-timeout=10s up
549ms
Error: dial tcp: lookup postgres.railway.internal on 169.254.169.254:53: no such host
```

The complete logs are attached here for reference:

```

[Region: us-west1]
 
╭─────────────────╮
│ Railpack 0.13.0 │
╰─────────────────╯
 
↳ Using config file `railpack.json`
⚠ The config file format is not yet finalized and subject to change.
↳ Found .dockerignore file, applying filters
↳ Detected Python
↳ Using uv
 
Packages
──────────
uv      │  0.9.11  │  railpack default (latest)
python  │  3.13.9  │  railpack default (3.13)
 
Steps
──────────
▸ install
$ curl -fsSL https://github.com/amacneil/dbmate/releases/latest/download/dbmate-linux-amd64 -o /usr/local/bin/dbmate && chmod +x /usr/local/bin/dbmate
 
▸ build
$ uv sync --locked --no-dev --no-editable
 
▸ migrate
$ dbmate --wait-timeout=10s up
 
Deploy
──────────
$ hypercorn main:app --bind "[::]:$PORT"

Successfully prepared Railpack plan for build

context: p552-Nko5

load build definition from railpack-plan.json
0ms

copy .python-version
78ms

install mise packages: python, uv
3s
mise uv@0.9.11 ✓ installed

curl -fsSL https://github.com/amacneil/dbmate/releases/latest/download/dbmate-linux-amd64 -o /usr/local/bin/dbmate && chmod +x /usr/local/bin/dbmate
990ms

copy /mise/shims, /mise/installs, / /app
1s

dbmate --wait-timeout=10s up
549ms
Error: dial tcp: lookup postgres.railway.internal on 169.254.169.254:53: no such host

uv sync --locked --no-dev --no-editable
450ms
runc run failed: container process is already dead

copy /usr/local/bin/mise
45ms
ERROR: failed to build: failed to solve: process "sh -c dbmate --wait-timeout=10s up" did not complete successfully: exit code: 2
```

passos · Accepted Answer

Hey, private networking is not available in the build process. Please add a pre-deploy command: <https://docs.railway.com/guides/pre-deploy-command#%5F%5Fnext>. Also, after that feel free to remove the `railpack.json` as it's not necessary.