32 KiB
+++ title = "Configuration file format" weight = 20 +++
Full example
Here is an example garage.toml
configuration file that illustrates all of the possible options:
replication_mode = "3"
metadata_dir = "/var/lib/garage/meta"
data_dir = "/var/lib/garage/data"
metadata_fsync = true
data_fsync = false
disable_scrub = false
metadata_auto_snapshot_interval = "6h"
db_engine = "lmdb"
block_size = "1M"
block_ram_buffer_max = "256MiB"
sled_cache_capacity = "128MiB"
sled_flush_every_ms = 2000
lmdb_map_size = "1T"
compression_level = 1
rpc_secret = "4425f5c26c5e11581d3223904324dcb5b5d5dfb14e5e7f35e38c595424f5f1e6"
rpc_bind_addr = "[::]:3901"
rpc_bind_outgoing = false
rpc_public_addr = "[fc00:1::1]:3901"
allow_world_readable_secrets = false
bootstrap_peers = [
"563e1ac825ee3323aa441e72c26d1030d6d4414aeb3dd25287c531e7fc2bc95d@[fc00:1::1]:3901",
"86f0f26ae4afbd59aaf9cfb059eefac844951efd5b8caeec0d53f4ed6c85f332@[fc00:1::2]:3901",
"681456ab91350f92242e80a531a3ec9392cb7c974f72640112f90a600d7921a4@[fc00:B::1]:3901",
"212fd62eeaca72c122b45a7f4fa0f55e012aa5e24ac384a72a3016413fa724ff@[fc00:F::1]:3901",
]
[consul_discovery]
api = "catalog"
consul_http_addr = "http://127.0.0.1:8500"
service_name = "garage-daemon"
ca_cert = "/etc/consul/consul-ca.crt"
client_cert = "/etc/consul/consul-client.crt"
client_key = "/etc/consul/consul-key.crt"
# for `agent` API mode, unset client_cert and client_key, and optionally enable `token`
# token = "abcdef-01234-56789"
tls_skip_verify = false
tags = [ "dns-enabled" ]
meta = { dns-acl = "allow trusted" }
[kubernetes_discovery]
namespace = "garage"
service_name = "garage-daemon"
skip_crd = false
[s3_api]
api_bind_addr = "[::]:3900"
s3_region = "garage"
root_domain = ".s3.garage"
[s3_web]
bind_addr = "[::]:3902"
root_domain = ".web.garage"
[admin]
api_bind_addr = "0.0.0.0:3903"
metrics_token = "BCAdFjoa9G0KJR0WXnHHm7fs1ZAbfpI8iIZ+Z/a2NgI="
admin_token = "UkLeGWEvHnXBqnueR3ISEMWpOnm40jH2tM2HnnL/0F4="
trace_sink = "http://localhost:4317"
The following gives details about each available configuration option.
Available configuration options
Index
Top-level configuration options:
allow_world_readable_secrets
,
block_ram_buffer_max
,
block_size
,
bootstrap_peers
,
compression_level
,
data_dir
,
data_fsync
,
db_engine
,
disable_scrub
,
lmdb_map_size
,
metadata_auto_snapshot_interval
,
metadata_dir
,
metadata_fsync
,
replication_mode
,
rpc_bind_addr
,
rpc_bind_outgoing
,
rpc_public_addr
,
rpc_secret
/rpc_secret_file
,
sled_cache_capacity
,
sled_flush_every_ms
.
The [consul_discovery]
section:
api
,
ca_cert
,
client_cert
,
client_key
,
consul_http_addr
,
meta
,
service_name
,
tags
,
tls_skip_verify
,
token
.
The [kubernetes_discovery]
section:
namespace
,
service_name
,
skip_crd
.
The [s3_api]
section:
api_bind_addr
,
root_domain
,
s3_region
.
The [s3_web]
section:
bind_addr
,
root_domain
.
The [admin]
section:
api_bind_addr
,
metrics_token
/metrics_token_file
,
admin_token
/admin_token_file
,
trace_sink
,
Environment variables
The following configuration parameter must be specified as an environment variable, it does not exist in the configuration file:
GARAGE_LOG_TO_SYSLOG
(since v0.9.4): set this to1
ortrue
to make the Garage daemon send its logs tosyslog
(using the libcsyslog
function) instead of printing to stderr.
The following environment variables can be used to override the corresponding values in the configuration file:
GARAGE_ALLOW_WORLD_READABLE_SECRETS
GARAGE_RPC_SECRET
andGARAGE_RPC_SECRET_FILE
GARAGE_ADMIN_TOKEN
andGARAGE_ADMIN_TOKEN_FILE
GARAGE_METRICS_TOKEN
andGARAGE_METRICS_TOKEN
Top-level configuration options
replication_mode
Garage supports the following replication modes:
-
none
or1
: data stored on Garage is stored on a single node. There is no redundancy, and data will be unavailable as soon as one node fails or its network is disconnected. Do not use this for anything else than test deployments. -
2
: data stored on Garage will be stored on two different nodes, if possible in different zones. Garage tolerates one node failure, or several nodes failing but all in a single zone (in a deployment with at least two zones), before losing data. Data remains available in read-only mode when one node is down, but write operations will fail.2-dangerous
: a variant of mode2
, where written objects are written to the second replica asynchronously. This means that Garage will return200 OK
to a PutObject request before the second copy is fully written (or even before it even starts being written). This means that data can more easily be lost if the node crashes before a second copy can be completed. This also means that written objects might not be visible immediately in read operations. In other words, this mode severely breaks the consistency and durability guarantees of standard Garage cluster operation. Benefits of this mode: you can still write to your cluster when one node is unavailable.
-
3
: data stored on Garage will be stored on three different nodes, if possible each in a different zones. Garage tolerates two node failure, or several node failures but in no more than two zones (in a deployment with at least three zones), before losing data. As long as only a single node fails, or node failures are only in a single zone, reading and writing data to Garage can continue normally.-
3-degraded
: a variant of replication mode3
, that lowers the read quorum to1
, to allow you to read data from your cluster when several nodes (or nodes in several zones) are unavailable. In this mode, Garage does not provide read-after-write consistency anymore. The write quorum is still 2, ensuring that data successfully written to Garage is stored on at least two nodes. -
3-dangerous
: a variant of replication mode3
that lowers both the read and write quorums to1
, to allow you to both read and write to your cluster when several nodes (or nodes in several zones) are unavailable. It is the least consistent mode of operation proposed by Garage, and also one that should probably never be used.
-
Note that in modes 2
and 3
,
if at least the same number of zones are available, an arbitrary number of failures in
any given zone is tolerated as copies of data will be spread over several zones.
Make sure replication_mode
is the same in the configuration files of all nodes.
Never run a Garage cluster where that is not the case.
The quorums associated with each replication mode are described below:
replication_mode |
Number of replicas | Write quorum | Read quorum | Read-after-write consistency? |
---|---|---|---|---|
none or 1 |
1 | 1 | 1 | yes |
2 |
2 | 2 | 1 | yes |
2-dangerous |
2 | 1 | 1 | NO |
3 |
3 | 2 | 2 | yes |
3-degraded |
3 | 2 | 1 | NO |
3-dangerous |
3 | 1 | 1 | NO |
Changing the replication_mode
between modes with the same number of replicas
(e.g. from 3
to 3-degraded
, or from 2-dangerous
to 2
), can be done easily by
just changing the replication_mode
parameter in your config files and restarting all your
Garage nodes.
It is also technically possible to change the replication mode to a mode with a
different numbers of replicas, although it's a dangerous operation that is not
officially supported. This requires you to delete the existing cluster layout
and create a new layout from scratch, meaning that a full rebalancing of your
cluster's data will be needed. To do it, shut down your cluster entirely,
delete the custer_layout
files in the meta directories of all your nodes,
update all your configuration files with the new replication_mode
parameter,
restart your cluster, and then create a new layout with all the nodes you want
to keep. Rebalancing data will take some time, and data might temporarily
appear unavailable to your users. It is recommended to shut down public access
to the cluster while rebalancing is in progress. In theory, no data should be
lost as rebalancing is a routine operation for Garage, although we cannot
guarantee you that everything will go right in such an extreme scenario.
metadata_dir
The directory in which Garage will store its metadata. This contains the node identifier, the network configuration and the peer list, the list of buckets and keys as well as the index of all objects, object version and object blocks.
Store this folder on a fast SSD drive if possible to maximize Garage's performance.
data_dir
The directory in which Garage will store the data blocks of objects.
This folder can be placed on an HDD. The space available for data_dir
should be counted to determine a node's capacity
when adding it to the cluster layout.
Since v0.9.0
, Garage supports multiple data directories with the following syntax:
data_dir = [
{ path = "/path/to/old_data", read_only = true },
{ path = "/path/to/new_hdd1", capacity = "2T" },
{ path = "/path/to/new_hdd2", capacity = "4T" },
]
See the dedicated documentation page on how to operate Garage in such a setup.
db_engine
(since v0.8.0
)
Since v0.8.0
, Garage can use alternative storage backends as follows:
DB engine | db_engine value |
Database path |
---|---|---|
LMDB (default since v0.9.0 ) |
"lmdb" |
<metadata_dir>/db.lmdb/ |
Sled (default up to v0.8.0 ) |
"sled" |
<metadata_dir>/db/ |
Sqlite | "sqlite" |
<metadata_dir>/db.sqlite |
Sled was the only database engine up to Garage v0.7.0. Performance issues and API limitations of Sled prompted the addition of alternative engines in v0.8.0. Since v0.9.0, LMDB is the default engine instead of Sled, and Sled is deprecated. We plan to remove Sled in Garage v1.0.
Performance characteristics of the different DB engines are as follows:
-
Sled: tends to produce large data files and also has performance issues, especially when the metadata folder is on a traditional HDD and not on SSD.
-
LMDB: the recommended database engine for high-performance distributed clusters, much more space-efficient and significantly faster. LMDB works very well, but is known to have the following limitations:
-
The data format of LMDB is not portable between architectures, so for instance the Garage database of an x86-64 node cannot be moved to an ARM64 node.
-
While LMDB can technically be used on 32-bit systems, this will limit your node to very small database sizes due to how LMDB works; it is therefore not recommended.
-
Several users have reported corrupted LMDB database files after an unclean shutdown (e.g. a power outage). This situation can generally be recovered from if your cluster is geo-replicated (by rebuilding your metadata db from other nodes), or if you have saved regular snapshots at the filesystem level.
-
-
Sqlite: Garage supports Sqlite as an alternative storage backend for metadata, which does not have the issues listed above for LMDB. On versions 0.8.x and earlier, Sqlite should be avoided due to abysmal performance, which was fixed with the addition of
metadata_fsync
. Sqlite is still probably slower than LMDB due to the way we use it, so it is not the best choice for high-performance storage clusters, but it should work fine in many cases.
It is possible to convert Garage's metadata directory from one format to another
using the garage convert-db
command, which should be used as follows:
garage convert-db -a <input db engine> -i <input db path> \
-b <output db engine> -o <output db path>
Make sure to specify the full database path as presented in the table above (third colummn), and not just the path to the metadata directory.
metadata_fsync
Whether to enable synchronous mode for the database engine or not.
This is disabled (false
) by default.
This reduces the risk of metadata corruption in case of power failures, at the cost of a significant drop in write performance, as Garage will have to pause to sync data to disk much more often (several times for API calls such as PutObject).
Using this option reduces the risk of simultaneous metadata corruption on several cluster nodes, which could lead to data loss.
If multi-site replication is used, this option is most likely not necessary, as it is extremely unlikely that two nodes in different locations will have a power failure at the exact same time.
(Metadata corruption on a single node is not an issue, the corrupted data file can always be deleted and reconstructed from the other nodes in the cluster.)
Here is how this option impacts the different database engines:
Database | metadata_fsync = false (default) |
metadata_fsync = true |
---|---|---|
Sled | default options | unsupported |
Sqlite | PRAGMA synchronous = OFF |
PRAGMA synchronous = NORMAL |
LMDB | MDB_NOMETASYNC + MDB_NOSYNC |
MDB_NOMETASYNC |
Note that the Sqlite database is always ran in WAL
mode (PRAGMA journal_mode = WAL
).
data_fsync
Whether to fsync
data blocks and their containing directory after they are
saved to disk.
This is disabled (false
) by default.
This might reduce the risk that a data block is lost in rare situations such as simultaneous node losing power, at the cost of a moderate drop in write performance.
Similarly to metatada_fsync
, this is likely not necessary
if geographical replication is used.
metadata_auto_snapshot_interval
(since Garage v0.9.4)
If this value is set, Garage will automatically take a snapshot of the metadata DB file at a regular interval and save it in the metadata directory. This can allow to recover from situations where the metadata DB file is corrupted, for instance after an unclean shutdown. See this page for details.
Garage keeps only the two most recent snapshots of the metadata DB and deletes older ones automatically.
Note that taking a metadata snapshot is a relatively intensive operation as the entire data file is copied. A snapshot being taken might have performance impacts on the Garage node while it is running. If the cluster is under heavy write load when a snapshot operation is running, this might also cause the database file to grow in size significantly as pages cannot be recycled easily. For this reason, it might be better to use filesystem-level snapshots instead if possible.
disable_scrub
By default, Garage runs a scrub of the data directory approximately once per month, with a random delay to avoid all nodes running at the same time. When it scrubs the data directory, Garage will read all of the data files stored on disk to check their integrity, and will rebuild any data files that it finds corrupted, using the remaining valid copies stored on other nodes. See this page for details.
Set the disable_scrub
configuration value to true
if you don't need Garage
to scrub the data directory, for instance if you are already scrubbing at the
filesystem level. Note that in this case, if you find a corrupted data file,
you should delete it from the data directory and then call garage repair blocks
on the node to ensure that it re-obtains a copy from another node on
the network.
block_size
Garage splits stored objects in consecutive chunks of size block_size
(except the last one which might be smaller). The default size is 1MiB and
should work in most cases. We recommend increasing it to e.g. 10MiB if
you are using Garage to store large files and have fast network connections
between all nodes (e.g. 1gbps).
If you are interested in tuning this, feel free to do so (and remember to report your findings to us!). When this value is changed for a running Garage installation, only files newly uploaded will be affected. Previously uploaded files will remain available. This however means that chunks from existing files will not be deduplicated with chunks from newly uploaded files, meaning you might use more storage space that is optimally possible.
block_ram_buffer_max
(since v0.9.4)
A limit on the total size of data blocks kept in RAM by S3 API nodes awaiting to be sent to storage nodes asynchronously.
Explanation: since Garage wants to tolerate node failures, it uses quorum writes to send data blocks to storage nodes: try to write the block to three nodes, and return ok as soon as two writes complete. So even if all three nodes are online, the third write always completes asynchronously. In general, there are not many writes to a cluster, and the third asynchronous write can terminate early enough so as to not cause unbounded RAM growth. However, if the S3 API node is continuously receiving large quantities of data and the third node is never able to catch up, many data blocks will be kept buffered in RAM as they are awaiting transfer to the third node.
The block_ram_buffer_max
sets a limit to the size of buffers that can be kept
in RAM in this process. When the limit is reached, backpressure is applied
back to the S3 client.
Note that this only counts buffers that have arrived to a certain stage of
processing (received from the client + encrypted and/or compressed as
necessary) and are ready to send to the storage nodes. Many other buffers will
not be counted and this is not a hard limit on RAM consumption. In particular,
if many clients send requests simultaneously with large objects, the RAM
consumption will always grow linearly with the number of concurrent requests,
as each request will use a few buffers of size block_size
for receiving and
intermediate processing before even trying to send the data to the storage
node.
The default value is 256MiB.
sled_cache_capacity
This parameter can be used to tune the capacity of the cache used by sled, the database Garage uses internally to store metadata. Tune this to fit the RAM you wish to make available to your Garage instance. This value has a conservative default (128MB) so that Garage doesn't use too much RAM by default, but feel free to increase this for higher performance.
sled_flush_every_ms
This parameters can be used to tune the flushing interval of sled. Increase this if sled is thrashing your SSD, at the risk of losing more data in case of a power outage (though this should not matter much as data is replicated on other nodes). The default value, 2000ms, should be appropriate for most use cases.
lmdb_map_size
This parameters can be used to set the map size used by LMDB, which is the size of the virtual memory region used for mapping the database file. The value of this parameter is the maximum size the metadata database can take. This value is not bound by the physical RAM size of the machine running Garage. If not specified, it defaults to 1GiB on 32-bit machines and 1TiB on 64-bit machines.
compression_level
Zstd compression level to use for storing blocks.
Values between 1
(faster compression) and 19
(smaller file) are standard compression
levels for zstd. From 20
to 22
, compression levels are referred as "ultra" and must be
used with extra care as it will use lot of memory. A value of 0
will let zstd choose a
default value (currently 3
). Finally, zstd has also compression designed to be faster
than default compression levels, they range from -1
(smaller file) to -99
(faster
compression).
If you do not specify a compression_level
entry, Garage will set it to 1
for you. With
this parameters, zstd consumes low amount of cpu and should work faster than line speed in
most situations, while saving some space and intra-cluster
bandwidth.
If you want to totally deactivate zstd in Garage, you can pass the special value 'none'
. No
zstd related code will be called, your chunks will be stored on disk without any processing.
Compression is done synchronously, setting a value too high will add latency to write queries.
This value can be different between nodes, compression is done by the node which receive the API call.
rpc_secret
, rpc_secret_file
or GARAGE_RPC_SECRET
, GARAGE_RPC_SECRET_FILE
(env)
Garage uses a secret key, called an RPC secret, that is shared between all
nodes of the cluster in order to identify these nodes and allow them to
communicate together. The RPC secret is a 32-byte hex-encoded random string,
which can be generated with a command such as openssl rand -hex 32
.
The RPC secret should be specified in the rpc_secret
configuration variable.
Since Garage v0.8.2
, the RPC secret can also be stored in a file whose path is
given in the configuration variable rpc_secret_file
, or specified as an
environment variable GARAGE_RPC_SECRET
.
Since Garage v0.8.5
and v0.9.1
, you can also specify the path of a file
storing the secret as the GARAGE_RPC_SECRET_FILE
environment variable.
rpc_bind_addr
The address and port on which to bind for inter-cluster communcations (reffered to as RPC for remote procedure calls). The port specified here should be the same one that other nodes will used to contact the node, even in the case of a NAT: the NAT should be configured to forward the external port number to the same internal port nubmer. This means that if you have several nodes running behind a NAT, they should each use a different RPC port number.
rpc_bind_outgoing
(since v0.9.2)
If enabled, pre-bind all sockets for outgoing connections to the same IP address
used for listening (the IP address specified in rpc_bind_addr
) before
trying to connect to remote nodes.
This can be necessary if a node has multiple IP addresses,
but only one is allowed or able to reach the other nodes,
for instance due to firewall rules or specific routing configuration.
Disabled by default.
rpc_public_addr
The address and port that other nodes need to use to contact this node for RPC calls. This parameter is optional but recommended. In case you have a NAT that binds the RPC port to a port that is different on your public IP, this field might help making it work.
bootstrap_peers
A list of peer identifiers on which to contact other Garage peers of this cluster. These peer identifiers have the following syntax:
<node public key>@<node public IP or hostname>:<port>
In the case where rpc_public_addr
is correctly specified in the
configuration file, the full identifier of a node including IP and port can
be obtained by running garage node id
and then included directly in the
bootstrap_peers
list of other nodes. Otherwise, only the node's public
key will be returned by garage node id
and you will have to add the IP
yourself.
allow_world_readable_secrets
or GARAGE_ALLOW_WORLD_READABLE_SECRETS
(env)
Garage checks the permissions of your secret files to make sure they're not world-readable. In some cases, the check might fail and consider your files as world-readable even if they're not, for instance when using Posix ACLs.
Setting allow_world_readable_secrets
to true
bypass this
permission verification.
Alternatively, you can set the GARAGE_ALLOW_WORLD_READABLE_SECRETS
environment variable to true
to bypass the permissions check.
The [consul_discovery]
section
Garage supports discovering other nodes of the cluster using Consul. For this
to work correctly, nodes need to know their IP address by which they can be
reached by other nodes of the cluster, which should be set in rpc_public_addr
.
consul_http_addr
The consul_http_addr
parameter should be set to the full HTTP(S) address of the Consul server.
api
Two APIs for service registration are supported: catalog
and agent
. catalog
, the default, will register a service using
the /v1/catalog
endpoints, enabling mTLS if client_cert
and client_key
are provided. The agent
API uses the
v1/agent
endpoints instead, where an optional token
may be provided.
service_name
service_name
should be set to the service name under which Garage's
RPC ports are announced.
client_cert
, client_key
TLS client certificate and client key to use when communicating with Consul over TLS. Both are mandatory when doing so.
Only available when api = "catalog"
.
ca_cert
TLS CA certificate to use when communicating with Consul over TLS.
tls_skip_verify
Skip server hostname verification in TLS handshake.
ca_cert
is ignored when this is set.
token
Uses the provided token for communication with Consul. Only available when api = "agent"
.
The policy assigned to this token should at least have these rules:
// the `service_name` specified above
service "garage" {
policy = "write"
}
service_prefix "" {
policy = "read"
}
node_prefix "" {
policy = "read"
}
tags
and meta
Additional list of tags and map of service meta to add during service registration.
The [kubernetes_discovery]
section
Garage supports discovering other nodes of the cluster using kubernetes custom
resources. For this to work, a [kubernetes_discovery]
section must be present
with at least the namespace
and service_name
parameters.
namespace
namespace
sets the namespace in which the custom resources are
configured.
service_name
service_name
is added as a label to the advertised resources to
filter them, to allow for multiple deployments in a single namespace.
skip_crd
skip_crd
can be set to true to disable the automatic creation and
patching of the garagenodes.deuxfleurs.fr
CRD. You will need to create the CRD
manually.
The [s3_api]
section
api_bind_addr
The IP and port on which to bind for accepting S3 API calls. This endpoint does not suport TLS: a reverse proxy should be used to provide it.
Alternatively, since v0.8.5
, a path can be used to create a unix socket with 0222 mode.
s3_region
Garage will accept S3 API calls that are targetted to the S3 region defined here. API calls targetted to other regions will fail with a AuthorizationHeaderMalformed error message that redirects the client to the correct region.
root_domain
The optional suffix to access bucket using vhost-style in addition to path-style request. Note path-style requests are always enabled, whether or not vhost-style is configured. Configuring vhost-style S3 required a wildcard DNS entry, and possibly a wildcard TLS certificate, but might be required by softwares not supporting path-style requests.
If root_domain
is s3.garage.eu
, a bucket called my-bucket
can be interacted with
using the hostname my-bucket.s3.garage.eu
.
The [s3_web]
section
Garage allows to publish content of buckets as websites. This section configures the behaviour of this module.
bind_addr
The IP and port on which to bind for accepting HTTP requests to buckets configured for website access. This endpoint does not suport TLS: a reverse proxy should be used to provide it.
Alternatively, since v0.8.5
, a path can be used to create a unix socket with 0222 mode.
root_domain
The optional suffix appended to bucket names for the corresponding HTTP Host.
For instance, if root_domain
is web.garage.eu
, a bucket called deuxfleurs.fr
will be accessible either with hostname deuxfleurs.fr.web.garage.eu
or with hostname deuxfleurs.fr
.
The [admin]
section
Garage has a few administration capabilities, in particular to allow remote monitoring. These features are detailed below.
api_bind_addr
If specified, Garage will bind an HTTP server to this port and address, on which it will listen to requests for administration features. See administration API reference to learn more about these features.
Alternatively, since v0.8.5
, a path can be used to create a unix socket. Note that for security reasons,
the socket will have 0220 mode. Make sure to set user and group permissions accordingly.
metrics_token
, metrics_token_file
or GARAGE_METRICS_TOKEN
, GARAGE_METRICS_TOKEN_FILE
(env)
The token for accessing the Metrics endpoint. If this token is not set, the Metrics endpoint can be accessed without access control.
You can use any random string for this value. We recommend generating a random token with openssl rand -base64 32
.
metrics_token
was introduced in Garage v0.7.2
.
metrics_token_file
and the GARAGE_METRICS_TOKEN
environment variable are supported since Garage v0.8.2
.
GARAGE_METRICS_TOKEN_FILE
is supported since v0.8.5
/ v0.9.1
.
admin_token
, admin_token_file
or GARAGE_ADMIN_TOKEN
, GARAGE_ADMIN_TOKEN_FILE
(env)
The token for accessing all of the other administration endpoints. If this token is not set, access to these endpoints is disabled entirely.
You can use any random string for this value. We recommend generating a random token with openssl rand -base64 32
.
admin_token
was introduced in Garage v0.7.2
.
admin_token_file
and the GARAGE_ADMIN_TOKEN
environment variable are supported since Garage v0.8.2
.
GARAGE_ADMIN_TOKEN_FILE
is supported since v0.8.5
/ v0.9.1
.
trace_sink
Optionally, the address of an OpenTelemetry collector. If specified, Garage will send traces in the OpenTelemetry format to this endpoint. These trace allow to inspect Garage's operation when it handles S3 API requests.