docs/vmalert.md: document multitenant support

https://github.com/VictoriaMetrics/VictoriaMetrics/issues/740

app/vmalert/README.md

@@ -176,6 +176,32 @@ in configured `-remoteRead.url`, weren't updated in the last `1h` or received st
 rules configuration.
 
 
+### Multitenancy
+
+There are the following approaches for alerting and recording rules across [multiple tenants](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#multitenancy) exist:
+
+* To run a separate `vmalert` instance per each tenant. The corresponding tenant must be specified in `-datasource.url` command-line flag according to [these docs](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#url-format). For example, `/path/to/vmalert -datasource.url=http://vmselect:8481/select/123/prometheus` would run alerts against `AccountID=123`. For recording rules the `-remoteWrite.url` command-line flag must contain the url for the specific tenant as well. For example, `-remoteWrite.url=http://vminsert:8480/insert/123/prometheus` would write recording rules to `AccountID=123`.
+
+* To specify `tenant` parameter per each alerting and recording group if [enterprise version of vmalert](https://victoriametrics.com/enterprise.html) is used with `-clusterMode` command-line flag. For example:
+
+```yaml
+groups:
+- name: rules_for_tenant_123
+  tenant: "123"
+  rules:
+    # Rules for accountID=123
+
+- name: rules_for_tenant_456:789
+  tenant: "456:789"
+  rules:
+    # Rules for accountID=456, projectID=789
+```
+
+If `-clusterMode` is enabled, then `-datasource.url`, `-remoteRead.url` and `-remoteWrite.url` must contain only the hostname without tenant id. For example: `-datasource.url=http://vmselect:8481` . `vmselect` automatically adds the specified tenant to urls per each recording rule in this case.
+
+The enterprise version of vmalert is available in `vmutils-*-enterprise.tar.gz` files at [release page](https://github.com/VictoriaMetrics/VictoriaMetrics/releases) and in `*-enterprise` tags at [Docker Hub](https://hub.docker.com/r/victoriametrics/vmalert/tags).
+
+
 ### WEB
 
 `vmalert` runs a web-server (`-httpListenAddr`) for serving metrics and alerts endpoints:

docs/CHANGELOG.md

@@ -4,6 +4,7 @@ sort: 15
 
 # CHANGELOG
 
+* FEATURE: vmalert: add ability to run alerting and recording rules for multiple tenants. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/740) and [these docs](https://docs.victoriametrics.com/vmalert.html#multitenancy).
 * FEATURE: vminsert: add support for data ingestion via other `vminsert` nodes. This allows building multi-level data ingestion paths in VictoriaMetrics cluster by writing data from one level of `vminsert` nodes to another level of `vminsert` nodes. See [these docs](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#multi-level-cluster-setup) and [this comment](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/541#issuecomment-835487858) for details.
 * FEATURE: vmagent: reload `bearer_token_file`, `credentials_file` and `password_file` contents every second. This allows dynamically changing the contents of these files during target scraping and service discovery without the need to restart `vmagent`. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1297).
 * FEATURE: vmalert: add flag to control behaviour on startup for state restore errors. Such errors were returned and logged before as well. But now user can specify whether to just log these errors (`-remoteRead.ignoreRestoreErrors=true`) or to stop the process (`-remoteRead.ignoreRestoreErrors=false`). The latter is important when VM isn't ready yet to serve queries from vmalert and it needs to wait. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1252).

docs/vmalert.md

@@ -180,6 +180,32 @@ in configured `-remoteRead.url`, weren't updated in the last `1h` or received st
 rules configuration.
 
 
+### Multitenancy
+
+There are the following approaches for alerting and recording rules across [multiple tenants](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#multitenancy) exist:
+
+* To run a separate `vmalert` instance per each tenant. The corresponding tenant must be specified in `-datasource.url` command-line flag according to [these docs](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#url-format). For example, `/path/to/vmalert -datasource.url=http://vmselect:8481/select/123/prometheus` would run alerts against `AccountID=123`. For recording rules the `-remoteWrite.url` command-line flag must contain the url for the specific tenant as well. For example, `-remoteWrite.url=http://vminsert:8480/insert/123/prometheus` would write recording rules to `AccountID=123`.
+
+* To specify `tenant` parameter per each alerting and recording group if [enterprise version of vmalert](https://victoriametrics.com/enterprise.html) is used with `-clusterMode` command-line flag. For example:
+
+```yaml
+groups:
+- name: rules_for_tenant_123
+  tenant: "123"
+  rules:
+    # Rules for accountID=123
+
+- name: rules_for_tenant_456:789
+  tenant: "456:789"
+  rules:
+    # Rules for accountID=456, projectID=789
+```
+
+If `-clusterMode` is enabled, then `-datasource.url`, `-remoteRead.url` and `-remoteWrite.url` must contain only the hostname without tenant id. For example: `-datasource.url=http://vmselect:8481` . `vmselect` automatically adds the specified tenant to urls per each recording rule in this case.
+
+The enterprise version of vmalert is available in `vmutils-*-enterprise.tar.gz` files at [release page](https://github.com/VictoriaMetrics/VictoriaMetrics/releases) and in `*-enterprise` tags at [Docker Hub](https://hub.docker.com/r/victoriametrics/vmalert/tags).
+
+
 ### WEB
 
 `vmalert` runs a web-server (`-httpListenAddr`) for serving metrics and alerts endpoints: