---
title: Sidecar
type: docs
menu: components
---

# Sidecar

The `thanos sidecar` command runs a component that gets deployed along with a Prometheus instance. This allows sidecar to optionally upload metrics to object storage and allow [Queriers](./query.md) to query Prometheus data with common, efficient StoreAPI.

In details:

* It implements Thanos' Store API on top of Prometheus' remote-read API. This allows [Queriers](./query.md) to treat Prometheus servers as yet another source of time series data without directly talking to its APIs.
* Optionally, the sidecar uploads TSDB blocks to an object storage bucket as Prometheus produces them every 2 hours. This allows Prometheus servers to be run with relatively low retention while their historic data is made durable and queryable via object storage.

  NOTE: This still does NOT mean that Prometheus can be fully stateless, because if it crashes and restarts you will lose ~2 hours of metrics, so persistent disk for Prometheus is highly recommended. The closest to stateless you can get is using remote write (which Thanos supports, see [Receiver](./receive.md). Remote write has other risks and consequences, and still if crashed you loose in positive case seconds of metrics data, so persistent disk is recommended in all cases.

* Optionally Thanos sidecar is able to watch Prometheus rules and configuration, decompress and substitute environment variables if needed and ping Prometheus to reload them. Read more about this in [here](./sidecar.md#reloader-configuration)

Prometheus servers connected to the Thanos cluster via the sidecar are subject to a few limitations and recommendations for safe operations:

* The recommended Prometheus version is 2.2.1 or greater (including newest releases). This is due to Prometheus instability in previous versions as well as lack of `flags` endpoint.
* (!) The Prometheus `external_labels` section of the Prometheus configuration file has unique labels in the overall Thanos system. Those external labels will be used by the sidecar and then Thanos in many places. See [external labels](../storage.md#external-labels) docs.
* The `--web.enable-admin-api` flag is enabled to support sidecar to get metadata from Prometheus like external labels.
* The `--web.enable-lifecycle` flag is enabled if you want to use sidecar reloading features (`--reload.*` flags).

If you choose to use the sidecar to also upload data to object storage:

* Must specify object storage (`--objstore.*` flags)
* It only uploads uncompacted Prometheus blocks. For compacted blocks, see [Upload compacted blocks](./sidecar.md/#upload-compacted-blocks).
* The `--storage.tsdb.min-block-duration` and `--storage.tsdb.max-block-duration` must be set to equal values to disable local compaction on order to use Thanos sidecar upload, otherwise leave local compaction on if sidecar just exposes StoreAPI and your retention is normal. The default of `2h` is recommended.
  Mentioned parameters set to equal values disable the internal Prometheus compaction, which is needed to avoid the uploaded data corruption when Thanos compactor does its job, this is critical for data consistency and should not be ignored if you plan to use Thanos compactor. Even though you set mentioned parameters equal, you might observe Prometheus internal metric `prometheus_tsdb_compactions_total` being incremented, don't be confused by that: Prometheus writes initial head block to filesytem via its internal compaction mechanism, but if you have followed recommendations - data won't be modified by Prometheus before the sidecar uploads it. Thanos sidecar will also check sanity of the flags set to Prometheus on the startup and log errors or warning if they have been configured improperly (#838).
* The retention is recommended to not be lower than three times the min block duration, so 6 hours. This achieves resilience in the face of connectivity issues to the object storage since all local data will remain available within the Thanos cluster. If connectivity gets restored the backlog of blocks gets uploaded to the object storage.

## Reloader Configuration

Thanos can watch changes in Prometheus configuration and refresh Prometheus configuration if `--web.enable-lifecycle` enabled.

You can configure watching for changes in directory via `--reloader.rule-dir=DIR_NAME` flag.

Thanos sidecar can watch `--reloader.config-file=CONFIG_FILE` configuration file, replace environment variables found in there in `$(VARIABLE)` format, and produce generated config in `--reloader.config-envsubst-file=OUT_CONFIG_FILE` file.

## Example basic deployment

```bash
prometheus \
  --storage.tsdb.max-block-duration=2h \
  --storage.tsdb.min-block-duration=2h \
  --web.enable-lifecycle
```

```bash
thanos sidecar \
    --tsdb.path        "/path/to/prometheus/data/dir" \
    --prometheus.url   "http://localhost:9090" \
    --objstore.config-file  "bucket.yml"
```

The example content of `bucket.yml`:

```yaml
type: GCS
config:
  bucket: example-bucket
```

## Upload compacted blocks

If you want to migrate from a pure Prometheus setup to Thanos and have to keep the historical data, you can use the flag `--shipper.upload-compacted`. This will also upload blocks that were compacted by Prometheus. Values greater than 1 in the `compaction.level` field of a Prometheus block’s `meta.json` file indicate level of compaction.

To use this, the Prometheus compaction needs to be disabled. This can be done by setting the following flags for Prometheus:

- `--storage.tsdb.min-block-duration=2h`
- `--storage.tsdb.max-block-duration=2h`

## Flags

[embedmd]:# (flags/sidecar.txt $)
```$
usage: thanos sidecar [<flags>]

Sidecar for Prometheus server.

Flags:
      --grpc-address="0.0.0.0:10901"
                                 Listen ip:port address for gRPC endpoints
                                 (StoreAPI). Make sure this address is routable
                                 from other components.
      --grpc-grace-period=2m     Time to wait after an interrupt received for
                                 GRPC Server.
      --grpc-server-tls-cert=""  TLS Certificate for gRPC server, leave blank to
                                 disable TLS
      --grpc-server-tls-client-ca=""
                                 TLS CA to verify clients against. If no client
                                 CA is specified, there is no client
                                 verification on server side. (tls.NoClientCert)
      --grpc-server-tls-key=""   TLS Key for the gRPC server, leave blank to
                                 disable TLS
      --hash-func=               Specify which hash function to use when
                                 calculating the hashes of produced files. If no
                                 function has been specified, it does not
                                 happen. This permits avoiding downloading some
                                 files twice albeit at some performance cost.
                                 Possible values are: "", "SHA256".
  -h, --help                     Show context-sensitive help (also try
                                 --help-long and --help-man).
      --http-address="0.0.0.0:10902"
                                 Listen host:port for HTTP endpoints.
      --http-grace-period=2m     Time to wait after an interrupt received for
                                 HTTP Server.
      --log.format=logfmt        Log format to use. Possible options: logfmt or
                                 json.
      --log.level=info           Log filtering level.
      --min-time=0000-01-01T00:00:00Z
                                 Start of time range limit to serve. Thanos
                                 sidecar will serve only metrics, which happened
                                 later than this value. Option can be a constant
                                 time in RFC3339 format or time duration
                                 relative to current time, such as -1d or 2h45m.
                                 Valid duration units are ms, s, m, h, d, w, y.
      --objstore.config=<content>
                                 Alternative to 'objstore.config-file' flag
                                 (mutually exclusive). Content of YAML file that
                                 contains object store configuration. See format
                                 details:
                                 https://thanos.io/tip/thanos/storage.md/#configuration
      --objstore.config-file=<file-path>
                                 Path to YAML file that contains object store
                                 configuration. See format details:
                                 https://thanos.io/tip/thanos/storage.md/#configuration
      --prometheus.ready_timeout=10m
                                 Maximum time to wait for the Prometheus
                                 instance to start up
      --prometheus.url=http://localhost:9090
                                 URL at which to reach Prometheus's API. For
                                 better performance use local network.
      --receive.connection-pool-size=RECEIVE.CONNECTION-POOL-SIZE
                                 Controls the http MaxIdleConns. Default is 0,
                                 which is unlimited
      --receive.connection-pool-size-per-host=100
                                 Controls the http MaxIdleConnsPerHost
      --reloader.config-envsubst-file=""
                                 Output file for environment variable
                                 substituted config file.
      --reloader.config-file=""  Config file watched by the reloader.
      --reloader.retry-interval=5s
                                 Controls how often reloader retries config
                                 reload in case of error.
      --reloader.rule-dir=RELOADER.RULE-DIR ...
                                 Rule directories for the reloader to refresh
                                 (repeated field).
      --reloader.watch-interval=3m
                                 Controls how often reloader re-reads config and
                                 rules.
      --request.logging-config=<content>
                                 Alternative to 'request.logging-config-file'
                                 flag (mutually exclusive). Content of YAML file
                                 with request logging configuration. See format
                                 details:
                                 https://gist.github.com/yashrsharma44/02f5765c5710dd09ce5d14e854f22825
      --request.logging-config-file=<file-path>
                                 Path to YAML file with request logging
                                 configuration. See format details:
                                 https://gist.github.com/yashrsharma44/02f5765c5710dd09ce5d14e854f22825
      --shipper.upload-compacted
                                 If true shipper will try to upload compacted
                                 blocks as well. Useful for migration purposes.
                                 Works only if compaction is disabled on
                                 Prometheus. Do it once and then disable the
                                 flag when done.
      --tracing.config=<content>
                                 Alternative to 'tracing.config-file' flag
                                 (mutually exclusive). Content of YAML file with
                                 tracing configuration. See format details:
                                 https://thanos.io/tip/thanos/tracing.md/#configuration
      --tracing.config-file=<file-path>
                                 Path to YAML file with tracing configuration.
                                 See format details:
                                 https://thanos.io/tip/thanos/tracing.md/#configuration
      --tsdb.path="./data"       Data directory of TSDB.
      --version                  Show application version.

```
