octodns-lexicon 0.1.dev4
Lexicon provider for OctoDNS
License: MIT

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# octodns-lexicon
Use Lexicon providers in OctoDNS

## Introduction
octodns_lexicon is a provider for OctoDNS which by acting as a wrapper, it lets you to use [Lexion](https://github.com/AnalogJ/lexicon) providers in [OctoDNS](https://github.com/github/octodns) and thus you can manage your DNS records as code across even more providers.

## Getting started
### Installation

    pip install octodns-lexicon
    
### Extra dependencies

Some providers has extra dependencies. These are not installed by default.

See [here](https://github.com/AnalogJ/lexicon#setup) for instructions on how to install extra dependencies for such providers.


### Configuration
From OctoDNS, this provider can be [configured](https://github.com/github/octodns#config) pretty much like any other, 

* `class`: `octodns_lexicon.LexiconProvider`
* `supports`: if defined, will limit the scope of the implemented record types: `{'A', 'AAAA', 'ALIAS', 'CAA', 'CNAME', 'MX', 'NS', 'SRV', 'TXT'}` (the *intersection* between implemented record types and provided list will be used)
* `lexicon_config`: lexicon config. This dictionary gets sent straight into the wrapped Lexicon provider as a [DictConfigSource](https://github.com/AnalogJ/lexicon/blob/master/lexicon/config.py#L269)

Furthermore: this provider also uses the Lexicon [EnvironmentConfigSource](https://github.com/AnalogJ/lexicon/blob/57a90f2c2992cb7c68371e05fb6d361c4b076374/lexicon/config.py#L217), so that you can put your lexicon dns providers settings into environment variables, just like in Lexicon.

The mandatory Lexicon command args such like `domain` will be provided at runtime, as that is populated from the source zone fed to it by OctoDNS. This means that same provider config can be used for multiple zones.


#### Example Configuration
```yaml
providers:
  gandi:
    class: octodns_lexicon.LexiconProvider
    supports:
      - A
      - AAAA
      - CNAME
      - MX
      - SRV
    lexicon_config:
      provider_name: gandi
      gandi:
        auth_token: "better kept in environment variable"
        api_protocol: rest

  namecheap:
    class: octodns_lexicon.LexiconProvider
    lexicon_config:
      provider_name: namecheap
      namecheap:
        auth_sandbox: True
        auth_username: foobar
        auth_client_ip: 127.0.0.1
        auth_token: "better kept in environment variable"
```
##### EnvironmentConfigSource

The `auth_token` for the namecheap provider in the example above could be put in environment variable `LEXICON_NAMECHEAP_AUTH_TOKEN` instead. (and for gandi it'd be `LEXICON_GANDI_AUTH_TOKEN`).


#### Supported Record types

Lexicon CLI handles the following record types: `A`, `AAAA`, `CNAME`, `MX`, `NS`, `SOA`, `TXT`, `SRV` and `LOC`. Of these `SOA` and `LOC` records have been omitted for various reasons and are not implemented. Instead, this provider has support for `CAA` records which seems to work well with most Lexicon providers.

The support for these above records varies between Lexicon providers, and they themselves do not indicate in standardized manner which of them would work. Therefore the operator can specify in `lexicon_config.supports` a subset of `{'A', 'AAAA', 'ALIAS', 'CAA', 'CNAME', 'MX', 'NS', 'SRV', 'TXT'}` and this provider will claim to support and try to apply that and nothing else, or leave blank to support the full set.

### Some words of caution on Lexicon providers

Some Lexicon providers is not well suited for use in OctoDNS. For example, not all providers support updating TTL once set, some do not handle multi value records. Others yet might have other unknown shortcomings which makes them unsuitable.

#### On record types in general

Most providers work well with `A`, `AAAA`, `TXT` and `CNAME` records, but there are few guarantees about other record types, and it's recommended to try and see and to not expect too much from a particular provider.

##### On SRV, MX and other record typpes with "multi-value values"

Record values might contain more than one data field, such like MX records, which contains preference value, and the fully qualified domain name of a mailserver. 
There are some inconsistencies in how lexicon providers handle these types of records. Some treats the additional value fields as extra options which they read from a Lexicon Config source while others handle them as single space separated value.

This provider uses the latter case, ie multi value values are treated as one joined with spaces, as this seems to be the most common case. 



#### On multi-value records
Lexicon handles multi value records as separate entities and by design cannot update a multi-value record in a single operation. This provider will try to deduce, for multi value records, which updated record belongs to a particular value by keeping track of all encountered ID:s (a mandatory Lexicon identifier) and on update call will target that ID. If that ID is not unique, then instead of update, it will run create and then delete operations. Depending on Lexicon provider implementation, this could lead to the provider running a big amount of API calls, and for big zones with many changes, this could lead to Rate limiting.

To deduce wether a particular provider is well suited or not, testing of the following in sandboxed environment is recommended best practice:

A good test case can be creating a multi-value A record (or whichever, really), and then to applying it with OctoDNS multiple times. Only the first run should apply any changes.

Second step could be to change some of the values for that record, and maybe add one or two values, but keep some intact, and then change TTL and apply that a couple of times. Only the first run should apply any changes.


### Also

#### On native OctoDNS providers

If there is a native OctoDNS provider available for a particular provider, then it is advisable to use that one and to not use the wrapped Lexicon equivalent, because some OctoDNS providers handle their DNS updates in atomic transactions, and others has geo DNS support. 
Also some providers handle updating a multi value record as a single operation whereas octodns_lexicon performs an update/create/create+delete per value.