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ipvsctl - User Documentation

Dynamic parameters

ipvsctl's model may contain dynamic parameters. Placeholders such as ${myvar} are read from a source other than the model file. Currently, valid source are OS environment, YAML and JSON files, and YAML and JSON data pulled via HTTP. Not all model elements may contain parameters. At present, only addresses (both in services and destinations) may contain parameters, which are resolved at runtime. A model entry is processed as a string and may contain multiple dynamic parameters. Parameters can embed other parameters (see examples below)

Command line switches to ipvsctl determine, from what sources parameters are pulled and resolved:

      --params-network   Dynamic parameters. Add every network interface name as resolvable ip address, e.g. net.eth0
      --params-env       Dynamic parameters. Add every environment entry, e.g. env.port=<ENV VAR "port">
      --params-file      Dynamic parameters. Add parameters from yaml or json file. (default [""])
      --params-url       Dynamic parameters. Add parameters from yaml or json resource given by URL. (default [""])

These switches become effective in conjunction with apply or validate commands. --params-file and --params-url may be specified multiple times, and are processed in that order (first entry found wins).

Parameter substitution uses ${ as the beginning marker and } as the end marker. So ${my.var} is valid whereas $other.{var} is not.

If the model contains a parameter which cannot by resolved by the sources given, the validation fails and ipvsctl terminates.

Parameters from Environment

When using --params-env, ipvsctl allows access to all environment entries, prepended by the env. prefix. E.g.

# MYPORT=8080 ADDR=1.2.3.4 ipvsctl --params-env apply

allows for the model file to contain an address element such as

    - address: tcp://${ADDR}:${MYPORT}

Parameters from local network

When using --params-network, ipvsctl allows access to the IP addresses of all network interfaces on the host, prepended by host., e.g.:

# ipvsctl --params-network apply

allows for the model file to contain an address element such as

    - address: tcp://${host.eth0}:80

In case a network adapter has more than one IP address, ipvsctl allows access to all of them by adding a zero-based index, e.g. - address: tcp://${host.eth0_1}:80 (eth0_1) resolves to the second address of the interface.

Parameters from files

When using --params-file, ipvsctl reads the given file, which must be JSON or YAML. All entries are made available, e.g.:

# cat p.yaml
ports:
  web: 8443
  api: 9443

# ipvsctl --params-files=p.yaml apply

allows for the model file to contain an address element such as

    - address: tcp://10.0.0.1:${ports.web}

--params-file may be specified multiple times.

Parameters from URLs

--params-url works similar to --params-file, but HTTP-GETs the YAML or JSON content from a url, e.g.:

# ipvsctl --params-url=http://my.config.local:8080/ apply

Nested parameters

Parameters may be nested, e.g.:

# cat p.yaml
backends:
  dev: localhost
  test: 192.168.1.10
  stage: 10.0.0.1

# CURENV=test ipvsctl --params-env --params-files=p.yaml apply

allows for

    - address: tcp://${backends.${CURENV}}:8080

CURENV resolves to test (from env), and thus backends.test resolves to 192.168.1.10 (from p.yaml), so the resulting line is

    - address: tcp://192.168.1.10:8080

This works in conjunction with all sources.