Merging upstream version 1.29.0.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+<!--
+title: "Use host labels to organize systems, metrics, and alarms"
+custom_edit_url: https://github.com/netdata/netdata/edit/master/docs/guides/using-host-labels.md
+-->
+
+# Use host labels to organize systems, metrics, and alarms
+
+When you use Netdata to monitor and troubleshoot an entire infrastructure, whether that's dozens or hundreds of systems,
+you need sophisticated ways of keeping everything organized. You need alarms that adapt to the system's purpose, or
+whether the parent or child in a streaming setup. You need properly-labeled metrics archiving so you can sort,
+correlate, and mash-up your data to your heart's content. You need to keep tabs on ephemeral Docker containers in a
+Kubernetes cluster.
+
+You need **host labels**: a powerful new way of organizing your Netdata-monitored systems. We introduced host labels in
+[v1.20 of Netdata](https://blog.netdata.cloud/posts/release-1.20/), and they come pre-configured out of the box.
+
+Let's take a peek into how to create host labels and apply them across a few of Netdata's features to give you more
+organization power over your infrastructure.
+
+## Create unique host labels
+
+Host labels are defined in `netdata.conf`. To create host labels, open that file using `edit-config`.
+
+```bash
+cd /etc/netdata   # Replace this path with your Netdata config directory, if different
+sudo ./edit-config netdata.conf
+```
+
+Create a new `[host labels]` section defining a new host label and its value for the system in question. Make sure not
+to violate any of the [host label naming rules](/docs/configuration-guide.md#netdata-labels).
+
+```conf
+[host labels]
+    type = webserver
+    location = us-seattle
+    installed = 20200218
+```
+
+Once you've written a few host labels, you need to enable them. Instead of restarting the entire Netdata service, you
+can reload labels using the helpful `netdatacli` tool:
+
+```bash
+netdatacli reload-labels
+```
+
+Your host labels will now be enabled. You can double-check these by using `curl http://HOST-IP:19999/api/v1/info` to
+read the status of your agent. For example, from a VPS system running Debian 10:
+
+```json
+{
+  ...
+  "host_labels": {
+    "_is_k8s_node": "false",
+    "_is_parent": "false",
+    "_virt_detection": "systemd-detect-virt",
+    "_container_detection": "none",
+    "_container": "unknown",
+    "_virtualization": "kvm",
+    "_architecture": "x86_64",
+    "_kernel_version": "4.19.0-6-amd64",
+    "_os_version": "10 (buster)",
+    "_os_name": "Debian GNU/Linux",
+    "type": "webserver",
+    "location": "seattle",
+    "installed": "20200218"
+  },
+  ...
+}
+```
+
+You may have noticed a handful of labels that begin with an underscore (`_`). These are automatic labels.
+
+### Automatic labels
+
+When Netdata starts, it captures relevant information about the system and converts them into automatically-generated
+host labels. You can use these to logically organize your systems via health entities, exporting metrics,
+parent-child status, and more.
+
+They capture the following:
+
+-   Kernel version
+-   Operating system name and version
+-   CPU architecture, system cores, CPU frequency, RAM, and disk space
+-   Whether Netdata is running inside of a container, and if so, the OS and hardware details about the container's host
+-   Whether Netdata is running inside K8s node 
+-   What virtualization layer the system runs on top of, if any
+-   Whether the system is a streaming parent or child
+
+If you want to organize your systems without manually creating host tags, try the automatic labels in some of the
+features below.
+
+## Host labels in streaming
+
+You may have noticed the `_is_parent` and `_is_child` automatic labels from above. Host labels are also now
+streamed from a child to its parent node, which concentrates an entire infrastructure's OS, hardware, container,
+and virtualization information in one place: the parent.
+
+Now, if you'd like to remind yourself of how much RAM a certain child node has, you can access
+`http://localhost:19999/host/CHILD_HOSTNAME/api/v1/info` and reference the automatically-generated host labels from the
+child system. It's a vastly simplified way of accessing critical information about your infrastructure.
+
+> ⚠️ Because automatic labels for child nodes are accessible via API calls, and contain sensitive information like
+> kernel and operating system versions, you should secure streaming connections with SSL. See the [streaming
+> documentation](/streaming/README.md#securing-streaming-communications) for details. You may also want to use
+> [access lists](/web/server/README.md#access-lists) or [expose the API only to LAN/localhost
+> connections](/docs/netdata-security.md#expose-netdata-only-in-a-private-lan).
+
+You can also use `_is_parent`, `_is_child`, and any other host labels in both health entities and metrics
+exporting. Speaking of which...
+
+## Host labels in health entities
+
+You can use host labels to logically organize your systems by their type, purpose, or location, and then apply specific
+alarms to them.
+
+For example, let's use configuration example from earlier:
+
+```conf
+[host labels]
+    type = webserver
+    location = us-seattle
+    installed = 20200218
+```
+
+You could now create a new health entity (checking if disk space will run out soon) that applies only to any host
+labeled `webserver`:
+
+```yaml
+    template: disk_fill_rate
+          on: disk.space
+      lookup: max -1s at -30m unaligned of avail
+        calc: ($this - $avail) / (30 * 60)
+       every: 15s
+ host labels: type = webserver
+```
+
+Or, by using one of the automatic labels, for only webserver systems running a specific OS:
+
+```yaml
+ host labels: _os_name = Debian*
+```
+
+In a streaming configuration where a parent node is triggering alarms for its child nodes, you could create health
+entities that apply only to child nodes:
+
+```yaml
+ host labels: _is_child = true
+```
+
+Or when ephemeral Docker nodes are involved:
+
+```yaml
+ host labels: _container = docker
+```
+
+Of course, there are many more possibilities for intuitively organizing your systems with host labels. See the [health
+documentation](/health/REFERENCE.md#alarm-line-host-labels) for more details, and then get creative!
+
+## Host labels in metrics exporting
+
+If you have enabled any metrics exporting via our experimental [exporters](/exporting/README.md), any new host
+labels you created manually are sent to the destination database alongside metrics. You can change this behavior by
+editing `exporting.conf`, and you can even send automatically-generated labels on with exported metrics.
+
+```conf
+[exporting:global]
+enabled = yes
+send configured labels = yes
+send automatic labels = no
+```
+
+You can also change this behavior per exporting connection:
+
+```conf
+[opentsdb:my_instance3]
+enabled = yes
+destination = localhost:4242
+data source = sum
+update every = 10
+send charts matching = system.cpu
+send configured labels = no
+send automatic labels = yes
+```
+
+By applying labels to exported metrics, you can more easily parse historical metrics with the labels applied. To learn
+more about exporting, read the [documentation](/exporting/README.md).
+
+## What's next?
+
+Host labels are a brand-new feature to Netdata, and yet they've already propagated deeply into some of its core
+functionality. We're just getting started with labels, and will keep the community apprised of additional functionality
+as it's made available. You can also track [issue #6503](https://github.com/netdata/netdata/issues/6503), which is where
+the Netdata team first kicked off this work.
+
+It should be noted that while the Netdata dashboard does not expose either user-configured or automatic host labels, API
+queries _do_ showcase this information. As always, we recommend you secure Netdata 
+
+-   [Expose Netdata only in a private LAN](/docs/netdata-security.md#expose-netdata-only-in-a-private-lan)
+-   [Enable TLS/SSL for web/API requests](/web/server/README.md#enabling-tls-support)
+-   Put Netdata behind a proxy
+    -   [Use an authenticating web server in proxy
+        mode](/docs/netdata-security.md#use-an-authenticating-web-server-in-proxy-mode)
+    -   [Nginx proxy](/docs/Running-behind-nginx.md)
+    -   [Apache proxy](/docs/Running-behind-apache.md)
+    -   [Lighttpd](/docs/Running-behind-lighttpd.md)
+    -   [Caddy](/docs/Running-behind-caddy.md)
+
+If you have issues or questions around using host labels, don't hesitate to [file an
+issue](https://github.com/netdata/netdata/issues/new?labels=bug%2C+needs+triage&template=bug_report.md) on GitHub. We're
+excited to make host labels even more valuable to our users, which we can only do with your input.
+
+[![analytics](https://www.google-analytics.com/collect?v=1&aip=1&t=pageview&_s=1&ds=github&dr=https%3A%2F%2Fgithub.com%2Fnetdata%2Fnetdata&dl=https%3A%2F%2Fmy-netdata.io%2Fgithub%2Fdocs%2Fguides%2Fusing-host-labels&_u=MAC~&cid=5792dfd7-8dc4-476b-af31-da2fdb9f93d2&tid=UA-64295674-3)](<>)