Smee

Smee is the network boot service in the Tinkerbell stack, formerly known as Boots. It is comprised of the following services.

• DHCP server
  • host reservations only
  • mac address based lookups
  • netboot options support
  • backend support
    • Kubernetes
    • file based
  • ProxyDHCP support
• TFTP server
  • serving iPXE binaries
• HTTP server
  • serving iPXE binaries and iPXE scripts
  • iPXE script serving uses IP authentication
  • backend support
    • Kubernetes
    • file based
• Syslog server
  • receives syslog messages and logs them

Definitions

DHCP Reservation: A fixed IP address that is reserved for a specific client.

DHCP Lease: An IP address, that can potentially change, that is assigned to a client by the DHCP server. The IP is typically pulled from a pool or subnet of available IP addresses.

ProxyDHCP: "[A] Proxy DHCP server behaves much like a DHCP server by listening for ordinary DHCP client traffic and responding to certain client requests. However, unlike the DHCP server, the PXE Proxy DHCP server does not administer network addresses, and it only responds to clients that identify themselves as PXE clients. The responses given by the PXE Proxy DHCP server contain the mechanism by which the client locates the boot servers or the network addresses and descriptions of the supported, compatible boot servers." -- IBM

Running Smee

DHCP Modes

Smee's DHCP functionality can operate in one of the following modes:

1. DHCP Reservation
   To enable this mode set -dhcp-mode=reservation. Smee will respond to DHCP requests from clients and provide them with IP and next boot info when netbooting. This is the default mode. IP info is all reservation based. There must be a corresponding Hardware record for the requesting client's MAC address.

2. Proxy DHCP
   To enable this mode set -dhcp-mode=proxy. Smee will respond to PXE enabled DHCP requests from clients and provide them with next boot info when netbooting. In this mode an existing DHCP server that does not serve network boot information is required. Smee will respond to PXE enabled DHCP requests and provide the client with the next boot info. There must be a corresponding Hardware record for the requesting client's MAC address. The auto.ipxe script will be served with the MAC address in the URL and the MAC address will be used to lookup the corresponding Hardware record. Layer 2 access to machines or a DHCP relay agent that will forward the DHCP requests to Smee is required.

3. Auto Proxy DHCP
   To enable this mode set -dhcp-mode=auto-proxy. Smee will respond to PXE enabled DHCP requests from clients and provide them with next boot info when netbooting. In this mode an existing DHCP server that does not serve network boot information is required. In this mode, if no corresponding Hardware record is found for the requesting client's MAC address, Smee will provide the client with a statically defined iPXE script. If a Hardware record is found, then the normal auto.ipxe script will be served. Use -backend-noop-enabled to disable all backend look ups. Layer 2 access to machines or a DHCP relay agent that will forward the DHCP requests to Smee is required.

   • When using Smee's auto.ipxe, you'll generally want to set the following flags:
     • -dhcp-mode=auto-proxy
     • -osie-url <URL to HookOS kernel and initrd>
     • -tink-server <IP and port of Tink server>
     • -extra-kernel-args="tink_worker_image=quay.io/tinkerbell/tink-worker:<use a version/commit tag>"
   • When not using Smee's auto.ipxe, you'll generally want to set the following flags:
     • -dhcp-mode=auto-proxy
     • -dhcp-http-ipxe-script-url=https://boot.netboot.xyz
     • -dhcp-http-ipxe-script-prepend-mac=false

4. DHCP disabled
   To enable this mode set -dhcp-enabled=false. Smee will not respond to DHCP requests from clients. This is useful when the network has an existing DHCP server that will provide both IP and next boot info and Smee's TFTP and HTTP functionality will be used. The IP address in the Hardware record must be the same as the IP address of the client requesting the auto.ipxe script. See this doc for more details. In most situations--dhcp-http-ipxe-script-prepend-mac=false should also be set when in this mode.

Interoperability with other DHCP servers

When a DHCP server exists on the network, Smee should be set to run proxy or auto-proxy mode. This will allow Smee to provide the next boot information to clients that request it. The existing DHCP server will provide the IP address and other network boot details. Layer 2 access to machines or a DHCP relay agent that will forward the DHCP requests to Smee is required.

It is not recommended, but it is possible for Smee to be run in reservation mode in networks with another DHCP server(s). To get the intended behavior from Smee one of the following must be true.

1. All DHCP servers besides Smee are configured to ignore the MAC addresses that Smee is configured to serve.

2. All DHCP servers are configured to serve the same IP address and network boot details as Smee. In this scenario the DHCP functionality of Smee is redundant. It would be recommended to run Smee with the DHCP server functionality disabled (-dhcp=false). See the doc on using your existing DHCP service for more details.

Environment Variables and CLI Flags

It's important to note that CLI flags take precedence over environment variables. All CLI flags can be set as environment variables. Environment variable names are the same as the flag names with some modifications. For example, the flag -dhcp-addr has the environment variable of SMEE_DHCP_ADDR. The modifications of CLI flags to environment variables are as follows:

• prefixed with SMEE_
• all uppercase
• hyphens (-) are replaced with underscores (_)

There is one environment variable that does not have a corresponding CLI flag. The environment variable is SMEE_PUBLIC_IP_INTERFACE. This environment variable takes a local network interface name and uses it to auto detect the IP address to use as the default in all other CLI flags that require an IP address. This is useful when the machine running Smee has multiple network interfaces and you want the default detected IP to be from this specified interface.

Local Setup

Running the Tests

# run the tests
make test

Build/Run Smee

# make the binary
make build
# run Smee
./smee -h

Smee is the DHCP and Network boot service for use in the Tinkerbell stack.

USAGE
  smee [flags]

FLAGS
  -log-level                          log level (debug, info) (default "info")
  -backend-file-enabled               [backend] enable the file backend for DHCP and the HTTP iPXE script (default "false")
  -backend-file-path                  [backend] the hardware yaml file path for the file backend
  -backend-kube-api                   [backend] the Kubernetes API URL, used for in-cluster client construction, kube backend only
  -backend-kube-config                [backend] the Kubernetes config file location, kube backend only
  -backend-kube-enabled               [backend] enable the kubernetes backend for DHCP and the HTTP iPXE script (default "true")
  -backend-kube-namespace             [backend] an optional Kubernetes namespace override to query hardware data from, kube backend only
  -backend-noop-enabled               [backend] enable the noop backend for DHCP and the HTTP iPXE script (default "false")
  -dhcp-addr                          [dhcp] local IP:Port to listen on for DHCP requests (default "0.0.0.0:67")
  -dhcp-enabled                       [dhcp] enable DHCP server (default "true")
  -dhcp-http-ipxe-binary-host         [dhcp] HTTP iPXE binaries host or IP to use in DHCP packets (default "172.17.0.3")
  -dhcp-http-ipxe-binary-path         [dhcp] HTTP iPXE binaries path to use in DHCP packets (default "/ipxe/")
  -dhcp-http-ipxe-binary-port         [dhcp] HTTP iPXE binaries port to use in DHCP packets (default "8080")
  -dhcp-http-ipxe-binary-scheme       [dhcp] HTTP iPXE binaries scheme to use in DHCP packets (default "http")
  -dhcp-http-ipxe-script-host         [dhcp] HTTP iPXE script host or IP to use in DHCP packets (default "172.17.0.3")
  -dhcp-http-ipxe-script-path         [dhcp] HTTP iPXE script path to use in DHCP packets (default "/auto.ipxe")
  -dhcp-http-ipxe-script-port         [dhcp] HTTP iPXE script port to use in DHCP packets (default "8080")
  -dhcp-http-ipxe-script-prepend-mac  [dhcp] prepend the hardware MAC address to iPXE script URL base, http://1.2.3.4/auto.ipxe -> http://1.2.3.4/40:15:ff:89:cc:0e/auto.ipxe (default "true")
  -dhcp-http-ipxe-script-scheme       [dhcp] HTTP iPXE script scheme to use in DHCP packets (default "http")
  -dhcp-http-ipxe-script-url          [dhcp] HTTP iPXE script URL to use in DHCP packets, this overrides the flags for dhcp-http-ipxe-script-{scheme, host, port, path}
  -dhcp-iface                         [dhcp] interface to bind to for DHCP requests
  -dhcp-ip-for-packet                 [dhcp] IP address to use in DHCP packets (opt 54, etc) (default "172.17.0.3")
  -dhcp-mode                          [dhcp] DHCP mode (reservation, proxy, auto-proxy) (default "reservation")
  -dhcp-syslog-ip                     [dhcp] Syslog server IP address to use in DHCP packets (opt 7) (default "172.17.0.3")
  -dhcp-tftp-ip                       [dhcp] TFTP server IP address to use in DHCP packets (opt 66, etc) (default "172.17.0.3")
  -dhcp-tftp-port                     [dhcp] TFTP server port to use in DHCP packets (opt 66, etc) (default "69")
  -extra-kernel-args                  [http] extra set of kernel args (k=v k=v) that are appended to the kernel cmdline iPXE script
  -http-addr                          [http] local IP to listen on for iPXE HTTP script requests (default "172.17.0.3")
  -http-ipxe-binary-enabled           [http] enable iPXE HTTP binary server (default "true")
  -http-ipxe-script-enabled           [http] enable iPXE HTTP script server (default "true")
  -http-port                          [http] local port to listen on for iPXE HTTP script requests (default "8080")
  -ipxe-script-retries                [http] number of retries to attempt when fetching kernel and initrd files in the iPXE script (default "0")
  -ipxe-script-retry-delay            [http] delay (in seconds) between retries when fetching kernel and initrd files in the iPXE script (default "2")
  -osie-url                           [http] URL where OSIE (HookOS) images are located
  -tink-server                        [http] IP:Port for the Tink server
  -tink-server-tls                    [http] use TLS for Tink server (default "false")
  -trusted-proxies                    [http] comma separated list of trusted proxies in CIDR notation
  -iso-enabled                        [iso] enable serving Hook as an iso (default "false")
  -iso-magic-string                   [iso] the string pattern to match for in the source iso, if not set the default from HookOS is used
  -iso-url                            [iso] the url for source iso before binary patching
  -otel-endpoint                      [otel] OpenTelemetry collector endpoint
  -otel-insecure                      [otel] OpenTelemetry collector insecure (default "true")
  -syslog-addr                        [syslog] local IP to listen on for Syslog messages (default "172.17.0.3")
  -syslog-enabled                     [syslog] enable Syslog server(receiver) (default "true")
  -syslog-port                        [syslog] local port to listen on for Syslog messages (default "514")
  -ipxe-script-patch                  [tftp/http] iPXE script fragment to patch into served iPXE binaries served via TFTP or HTTP
  -tftp-addr                          [tftp] local IP to listen on for iPXE TFTP binary requests (default "172.17.0.3")
  -tftp-block-size                    [tftp] TFTP block size a value between 512 (the default block size for TFTP) and 65456 (the max size a UDP packet payload can be) (default "512")
  -tftp-enabled                       [tftp] enable iPXE TFTP binary server) (default "true")
  -tftp-port                          [tftp] local port to listen on for iPXE TFTP binary requests (default "69")
  -tftp-timeout                       [tftp] iPXE TFTP binary server requests timeout (default "5s")

Developing using the file backend

The quickest way to get started is docker-compose up. This will start Smee using the file backend. This uses the example Yaml file (hardware.yaml) in the test/ directory. It also starts a client container that runs some tests.

docker compose up --build   # build images and start the network & services
# it's fine to hit control-C twice for fast shutdown
docker compose down  # stop the network & containers

Alternatively Smee can be run by itself. It requires a few flags or environment variables for configuration.

test/hardware.yaml should be safe enough for most developers to use on the command line locally without getting a call from your network administrator. That said, you might want to contact them before running a DHCP server on their network. Best to isolate it in Docker or a VM if you're not sure.

# build the binary
make build

export SMEE_OSIE_URL=<http url to the OSIE (Operating System Installation Environment) artifacts>
# For more info on the default OSIE (Hook) artifacts, please see https://github.com/tinkerbell/hook
export SMEE_BACKEND_KUBE_ENABLED=false
export SMEE_BACKEND_FILE_ENABLED=true
export SMEE_BACKEND_FILE_PATH=./test/hardware.yaml
export SMEE_EXTRA_KERNEL_ARGS="tink_worker_image=quay.io/tinkerbell/tink-worker:latest"

# By default, Smee needs to bind to low ports (67, 69, 514) so it needs root.
sudo -E ./cmd/smee/smee

# clean up the environment variables
unset SMEE_OSIE_URL
unset SMEE_BACKEND_KUBE_ENABLED
unset SMEE_BACKEND_FILE_ENABLED
unset SMEE_BACKEND_FILE_PATH
unset SMEE_EXTRA_KERNEL_ARGS