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Add documentation for /traefik/alias.

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Advait Shinde 2016-02-15 18:46:03 -05:00
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@ -15,6 +15,7 @@ ___
- [Etcd backend](#etcd)
- [Zookeeper backend](#zk)
- [Boltdb backend](#boltdb)
- [Atomic configuration changes](#atomicconfig)
- [Benchmarks](#benchmarks)
@ -946,6 +947,44 @@ Træfɪk can be configured to use BoltDB as a backend configuration:
# filename = "boltdb.tmpl"
```
## <a id="atomicconfig"></a> Atomic configuration changes
The [Etcd](https://github.com/coreos/etcd/issues/860) and [Consul](https://github.com/hashicorp/consul/issues/886) backends do not support updating multiple keys atomically. As a result, it may be possible for Træfɪk to read an intermediate configuration state despite judicious use of the `--providersThrottleDuration` flag. To solve this problem, Træfɪk supports a special key called `/traefik/alias`. If set, Træfɪk use the value as an alternative key prefix.
Given the key structure below, Træfɪk will use the `http://172.17.0.2:80` as its only backend (frontend keys have been omitted for brevity).
| Key | Value |
|-------------------------------------------------------------------------|-----------------------------|
| `/traefik/alias` | `/traefik_configurations/1` |
| `/traefik_configurations/1/backends/backend1/servers/server1/url` | `http://172.17.0.2:80` |
| `/traefik_configurations/1/backends/backend1/servers/server1/weight` | `10` |
When an atomic configuration change is required, you may write a new configuration at an alternative prefix. Here, although the `/traefik_configurations/2/...` keys have been set, the old configuration is still active because the `/traefik/alias` key still points to `/traefik_configurations/1`:
| Key | Value |
|-------------------------------------------------------------------------|-----------------------------|
| `/traefik/alias` | `/traefik_configurations/1` |
| `/traefik_configurations/1/backends/backend1/servers/server1/url` | `http://172.17.0.2:80` |
| `/traefik_configurations/1/backends/backend1/servers/server1/weight` | `10` |
| `/traefik_configurations/2/backends/backend1/servers/server1/url` | `http://172.17.0.2:80` |
| `/traefik_configurations/2/backends/backend1/servers/server1/weight` | `5` |
| `/traefik_configurations/2/backends/backend1/servers/server2/url` | `http://172.17.0.3:80` |
| `/traefik_configurations/2/backends/backend1/servers/server2/weight` | `5` |
Once the `/traefik/alias` key is updated, the new `/traefik_configurations/2` configuration becomes active atomically. Here, we have a 50% balance between the `http://172.17.0.3:80` and the `http://172.17.0.4:80` hosts while no traffic is sent to the `172.17.0.2:80` host:
| Key | Value |
|-------------------------------------------------------------------------|-----------------------------|
| `/traefik/alias` | `/traefik_configurations/2` |
| `/traefik_configurations/1/backends/backend1/servers/server1/url` | `http://172.17.0.2:80` |
| `/traefik_configurations/1/backends/backend1/servers/server1/weight` | `10` |
| `/traefik_configurations/2/backends/backend1/servers/server1/url` | `http://172.17.0.3:80` |
| `/traefik_configurations/2/backends/backend1/servers/server1/weight` | `5` |
| `/traefik_configurations/2/backends/backend1/servers/server2/url` | `http://172.17.0.4:80` |
| `/traefik_configurations/2/backends/backend1/servers/server2/weight` | `5` |
Note that TRAEFIK *will not watch for key changes in the `/traefik_configurations` prefix*. It will only watch for changes in the `/traefik` prefix. Further, if the `/traefik/alias` key is set, all other sibling keys with the `/traefik` prefix are ignored.
## <a id="benchmarks"></a> Benchmarks