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136 lines
4.4 KiB
Markdown
136 lines
4.4 KiB
Markdown
---
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layout: default
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title: CLI variables
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---
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# CLI variables
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You can pass variables into your configuration from the command line using the `-v key=value` flag. There is also a mechanism called `CLI_DEFAULTS` which lets you easily set the defaults on variables that are otherwise controlled from the command line.
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This gives you the opportunity to run different code when a value is passed.
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## Passing variables
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To pass a variable from CLI, just use the parameter `-v key=value` when using subcommands `preview` or `push`.
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Example: `dnscontrol preview -v testKey=testValue`
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This would set the variable with the name `testKey` and the value of `testValue` when processing `dnsconfig.js`
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## Define defaults
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The `CLI_DEFAULTS` feature is used to define default values for when a variable is not defined on the command line.
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```js
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CLI_DEFAULTS({
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"variableName": "defaultValue",
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});
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```
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You need to define this defaults just once in your `dnsconfig.js`. It should be defined **before** using it.
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_Please keep in mind that accessing an undefined variable is an error. If it is not set on the command line nor in `CLI_DEFAULTS`, accessing the variable will fail._
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## Example 1: Different IPs for internal/external DNS
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In this example we have a number of variables which need to be set differently when `view=internal`.
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In this configuration:
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* `dnscontrol push` would generate the external (default) view.
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* `dnscontrol push -v view=internal` would generate the internal view.
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```js
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// See https://stackexchange.github.io/dnscontrol/cli-variables
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CLI_DEFAULTS({
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"view": "external",
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});
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if (view == "external") {
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// BIND view: external (192.168.0.0/16 addresses)
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var host01 = "192.168.0.16";
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var host02 = "192.168.0.17";
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} else {
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// BIND view: internal (10.0.0.0/8 addresses)
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var host01 = "10.0.0.16";
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var host02 = "10.0.0.17";
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}
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/// ...much later...
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D("example.org", REG_NAMECOM, DnsProvider(DNS_NAMECOM), DnsProvider(DNS_BIND),
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A("sitea", host01, TTL(1800)),
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A("siteb", host01, TTL(1800)),
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A("sitec", host02, TTL(1800)),
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A("sited", host02, TTL(1800))
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);
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```
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## Example 2: Different DNS records
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In this example different code is run when `emergency=true`. Normally
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`server12` is an A record but in an emergency it is a CNAME.
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In this configuration:
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* `dnscontrol push` would generate the normal configuration.
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* `dnscontrol push -v emergency=true` would generate the emergency configuration.
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```js
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// See https://stackexchange.github.io/dnscontrol/cli-variables
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CLI_DEFAULTS({
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"emergency": false,
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});
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// ...much later...
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D("example.com", REG_EXAMPLE, DnsProvider(DNS_EXAMPLE),
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A("www", "10.10.10.10"),
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);
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if (emergency) {
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// Emergency mode: Configure A/B/C using CNAMEs to our alternate site.
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D_EXTEND("example.com",
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CNAME("a", "a.othersite"),
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CNAME("b", "b.othersite"),
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CNAME("c", "c.othersite")
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);
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} else {
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// Normal operation: Configure A/B/C using A records.
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D_EXTEND("example.com",
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A("a", "10.10.10.10"),
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A("b", "10.10.10.11"),
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A("c", "10.10.10.12")
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);
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}
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```
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#### ProTips
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The cli variables functionality permits you to create very complex and
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sophisticated configurations, but you shouldn't. Be nice to the next person
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that edits the file, who may not be as expert as yourself.
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While there is no limit to the number of variables that can be set on the
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command line, doing so is annoying to the person using the tool. It is better
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to set one variables which specifies a "mode". This mode is then used to
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automatically set other variables. This way the user can determine the mode and
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the code can determine what to do in that mode. This is less error-prone and
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more testable.
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In the first example, you'll see that one variable is used to set a mode which
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then determines many other variables. This is done in one place, at the top of
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the file. Everything related to this is isolated to one place, thus easier to
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maintain. The rest of the file simply uses those variables.
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In the second example, you'll see a boolean variable is set which selects which
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code will run different code. While the conditional code is not isolated to the
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top of the file, the conditional code is placed immediately after the domain.
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In both examples, not setting any variables on the command line does something
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reasonable. If someone accidentally runs `dnscontrol push` without any
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variables, the behavior is correct (assuming we're not in emergency mode, which
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is unlikely).
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