0844adbcbe
<message>Modify the first-boot.sh script to include an additional step for managing screen brightness during the provisioning process. Update user-data.bootstrap to improve DNS configuration by ensuring NetworkManager manages /etc/resolv.conf correctly, and remove obsolete scripts related to systemd-resolved. Enhance documentation to reflect these changes and clarify the setup process for users, improving overall network boot functionality and user experience.
91 lines
4.7 KiB
Markdown
91 lines
4.7 KiB
Markdown
# Device DNS from DHCP and /etc/resolv.conf
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This document describes how to configure provisioned devices (e.g. Raspberry Pi / reTerminal) so they **use DNS from DHCP** and do **not** have a fixed nameserver in `/etc/resolv.conf`. That way the LXC’s dnsmasq (option 6) is used, **file.server** resolves, and scripts can use `http://file.server/...` without hardcoding IPs.
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## Summary of changes (what we did on the Pi)
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1. **Do not overwrite `/etc/resolv.conf`**
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No script (e.g. bootstrap or first-boot) should write a fixed nameserver (e.g. `8.8.8.8`) into `/etc/resolv.conf`. DNS should come from DHCP.
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2. **LXC sends DHCP option 6 (DNS server)**
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dnsmasq on the LXC must send the LXC’s eth1 IP as the DNS server so clients use it and get **file.server** resolution. See [DNSMASQ-DNS-FILESERVER.md](DNSMASQ-DNS-FILESERVER.md) and `scripts/setup-network-boot-on-lxc.sh` (`dhcp-option=6,${LAN_GW}`).
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3. **Let NetworkManager manage `/etc/resolv.conf`**
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So that the nameserver in `/etc/resolv.conf` is the one from DHCP (option 6), either:
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- **Option A (recommended for full cloud-init):** Use **systemd-resolved** and make `/etc/resolv.conf` a symlink to the resolved stub; resolved gets DNS from NetworkManager.
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- **Option B (minimal cloud-init):** Use **NetworkManager** to manage `/etc/resolv.conf` via a symlink: add `rc-manager=symlink` in NetworkManager config so `/etc/resolv.conf` points to `/run/NetworkManager/resolv.conf`, which NM fills with the DHCP DNS.
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4. **Ensure connection uses DHCP DNS**
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The NetworkManager connection should have `ipv4.ignore-auto-dns: no` (default) so it accepts option 6 from DHCP. No fixed `ipv4.dns` in the connection.
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## What to change in cloud-init
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### Option A: user-data.bootstrap (uses Option B for RPi OS)
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**File:** `cloud-init/user-data.bootstrap`
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- **manage_resolv_conf: false** — already set; cloud-init must not overwrite resolv.conf.
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- **NetworkManager** — `99-resolv-dhcp.conf` has `rc-manager=symlink` so NM creates `/etc/resolv.conf` with DHCP DNS. RPi OS does not use systemd-resolved by default.
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- **runcmd** — removes static resolv.conf and restarts NM so it creates the symlink with DHCP option 6.
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- **Bootstrap script** — must **not** write `nameserver 8.8.8.8` (or any fixed server) into `/etc/resolv.conf`. Our `bootstrap.sh` no longer does that.
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No extra changes needed if you use `user-data.bootstrap` as-is; just ensure your bootstrap script does not touch resolv.conf.
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### Option B: Minimal user-data (first-boot or bootstrap-only, no systemd-resolved)
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If your user-data only runs a remote script (e.g. `first-boot.sh` or `bootstrap.sh`) and does **not** enable systemd-resolved, add the following so the device uses DNS from DHCP and NM manages resolv.conf:
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1. **Set in user-data (cloud-config):**
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```yaml
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manage_resolv_conf: false
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```
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2. **Add a write_files entry** so NetworkManager manages resolv.conf with the DHCP-provided DNS:
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```yaml
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write_files:
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# ... your other write_files ...
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- path: /etc/NetworkManager/conf.d/99-resolv-dhcp.conf
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content: |
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[main]
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rc-manager=symlink
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permissions: '0644'
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```
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3. **In your bootstrap/first-boot script:**
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Do **not** write a fixed nameserver to `/etc/resolv.conf` (e.g. remove any line like `echo "nameserver 8.8.8.8" > /etc/resolv.conf`).
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4. **Optional runcmd** (if you want a clean state on first boot):
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Remove any existing static resolv.conf so NM can create its symlink and write DHCP DNS:
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```yaml
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runcmd:
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- rm -f /etc/resolv.conf
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- systemctl restart NetworkManager
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# ... then your download and run of bootstrap.sh or first-boot.sh ...
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```
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After first boot, devices will get DNS from DHCP (LXC option 6), and **file.server** will resolve to the LXC’s eth1 IP.
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## Verification on the device
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```bash
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# Should show the LXC as nameserver (e.g. 10.20.40.1), not 8.8.8.8
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cat /etc/resolv.conf
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# Should resolve to LXC eth1
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getent hosts file.server
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```
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## Reference: manual fix on an already-provisioned device
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If a device was provisioned before these changes and still has a fixed DNS (e.g. 8.8.8.8):
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1. **LXC:** Ensure dnsmasq sends option 6 (see [DNSMASQ-DNS-FILESERVER.md](DNSMASQ-DNS-FILESERVER.md)); re-run `setup-network-boot-on-lxc.sh` if needed.
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2. **On the device:**
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- Add NetworkManager config:
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`echo -e '[main]\nrc-manager=symlink' | sudo tee /etc/NetworkManager/conf.d/99-resolv-dhcp.conf`
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- Remove static resolv.conf and restart NM:
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`sudo rm -f /etc/resolv.conf && sudo systemctl restart NetworkManager`
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- Renew DHCP so the device gets option 6:
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`sudo nmcli con down "Wired connection 1"; sudo nmcli con up "Wired connection 1"`
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3. Check: `cat /etc/resolv.conf` and `getent hosts file.server`.
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