ArangoDB Server Server Options

Managing Endpoints

The ArangoDB server can listen for incoming requests on multiple endpoints.

The endpoints are normally specified either in ArangoDB’s configuration file or on the command-line like --server.endpoint. ArangoDB supports different types of endpoints:

• tcp://ipv4-address:port - TCP/IP endpoint, using IPv4
• tcp://[ipv6-address]:port - TCP/IP endpoint, using IPv6
• ssl://ipv4-address:port - TCP/IP endpoint, using IPv4, SSL encryption
• ssl://[ipv6-address]:port - TCP/IP endpoint, using IPv6, SSL encryption
• unix:///path/to/socket - Unix domain socket endpoint

If a TCP/IP endpoint is specified without a port number, then the default port (8529) will be used. If multiple endpoints need to be used, the option can be repeated multiple times.

The default endpoint for ArangoDB is tcp://127.0.0.1:8529 or tcp://localhost:8529.

Examples

unix> ./arangod --server.endpoint tcp://127.0.0.1:8529
                --server.endpoint ssl://127.0.0.1:8530
                --ssl.keyfile server.pem /tmp/vocbase
2019-05-06T07:30:42Z [9228] INFO ArangoDB 3.4.5 [linux] 64bit, using jemalloc, build tags/v3.4.5-0-g648fbb8191, VPack 0.1.33, RocksDB 5.16.0, ICU 58.1, V8 5.7.492.77, OpenSSL 1.1.0j  20 Nov 2018
2019-05-06T07:30:43Z [9228] INFO {authentication} Jwt secret not specified, generating...
2019-05-06T07:30:43Z [9228] INFO using storage engine rocksdb
2019-05-06T07:30:43Z [9228] INFO {cluster} Starting up with role SINGLE
2019-05-06T07:50:53Z [9228] INFO {syscall} file-descriptors (nofiles) hard limit is 1048576, soft limit is 1048576
2019-05-06T07:50:53Z [9228] INFO {authentication} Authentication is turned on (system only), authentication for unix sockets is turned on
2019-05-06T07:30:43Z [9228] INFO using endpoint 'http+tcp://127.0.0.1:8529' for non-encrypted requests
2019-05-06T07:30:43Z [9228] INFO using endpoint 'http+ssl://127.0.0.1:8530' for ssl-encrypted requests
2019-05-06T07:30:44Z [9228] INFO ArangoDB (version 3.4.5 [linux]) is ready for business. Have fun!

Given a hostname:

--server.endpoint tcp://hostname:port

Given an IPv4 address:

--server.endpoint tcp://ipv4-address:port

Given an IPv6 address:

--server.endpoint tcp://[ipv6-address]:port

On one specific ethernet interface each port can only be bound exactly once. You can look up your available interfaces using the ifconfig command on Linux / macOS - the Windows equivalent is ipconfig (see Wikipedia for more details). The general names of the interfaces differ on OS’s and hardwares they run on. However, typically every host has a so called loopback interface, which is a virtual interface. By convention it always has the address 127.0.0.1 or ::1 (ipv6), and can only be reached from exactly the very same host. Ethernet interfaces usually have names like eth0, wlan0, eth1:17, le0 or a plain text name in Windows.

To find out which services already use ports (so ArangoDB can’t bind them anymore), you can use the netstat command (it behaves a little different on each platform, run it with -lnpt on Linux, -p tcp on macOS or with -an on windows for valuable information).

ArangoDB can also do a so called broadcast bind using tcp://0.0.0.0:8529. This way it will be reachable on all interfaces of the host. This may be useful on development systems that frequently change their network setup like laptops.

Special note on IPv6 link-local addresses

ArangoDB can also listen to IPv6 link-local addresses via adding the zone ID to the IPv6 address in the form [ipv6-link-local-address%zone-id]. However, what you probably instead want is to bind to a local IPv6 address. Local IPv6 addresses start with fd. If you only see a fe80: IPv6 address in your interface configuration but no IPv6 address starting with fd your interface has no local IPv6 address assigned. You can read more about IPv6 link-local addresses here.

Example

Bind to a link-local and local IPv6 address.

unix> ifconfig

This command lists all interfaces and assigned ip addresses. The link-local address may be fe80::6257:18ff:fe82:3ec6%eth0 (IPv6 address plus interface name). A local IPv6 address may be fd12:3456::789a. To bind ArangoDB to it start arangod with --server.endpoint tcp://[fe80::6257:18ff:fe82:3ec6%eth0]:8529. Use telnet to test the connection.

unix> telnet fe80::6257:18ff:fe82:3ec6%eth0 8529
Trying fe80::6257:18ff:fe82:3ec6...
Connected to my-machine.
Escape character is '^]'.
GET / HTTP/1.1

HTTP/1.1 301 Moved Permanently
Location: /_db/_system/_admin/aardvark/index.html
Content-Type: text/html
Server: ArangoDB
Connection: Keep-Alive
Content-Length: 197

<html><head><title>Moved</title></head><body><h1>Moved</h1><p>This page has moved to <a href="/_db/_system/_admin/aardvark/index.html">/_db/_system/_admin/aardvark/index.html</a>.</p></body></html>

Reuse address

--tcp.reuse-address

If this boolean option is set to true then the socket option SO_REUSEADDR is set on all server endpoints, which is the default. If this option is set to false it is possible that it takes up to a minute after a server has terminated until it is possible for a new server to use the same endpoint again. This is why this is activated by default.

Please note however that under some operating systems this can be a security risk because it might be possible for another process to bind to the same address and port, possibly hijacking network traffic. Under Windows, ArangoDB additionally sets the flag SO_EXCLUSIVEADDRUSE as a measure to alleviate this problem.

Backlog size

--tcp.backlog-size

Allows to specify the size of the backlog for the listen system call The default value is 10. The maximum value is platform-dependent. Specifying a higher value than defined in the system header’s SOMAXCONN may result in a warning on server start. The actual value used by listen may also be silently truncated on some platforms (this happens inside the listen system call).

Maximal queue size

Maximum size of the queue for requests: --server.maximal-queue-size size

Specifies the maximum size of the queue for asynchronous task execution. If the queue already contains size tasks, new tasks will be rejected until other tasks are popped from the queue. Setting this value may help preventing an instance from being overloaded or from running out of memory if the queue is filled up faster than the server can process requests.

Scheduler queue unavailable fill grade

The startup option --server.unavailability-queue-fill-grade can be used to set a high-watermark for the scheduler’s queue fill grade, from which onwards the server will start reporting unavailability via its availability API.

This option has a consequence for the /_admin/server/availability REST API only, which is often called by load-balancers and other availability probing systems.

The /_admin/server/availability REST API will return HTTP 200 if the fill grade of the scheduler’s queue is below the configured value, or HTTP 503 if the fill grade is equal to or above it. This can be used to flag a server as unavailable in case it is already highly loaded.

The default value for this option is 0.75 since ArangoDB 3.8, i.e. 75%.

To prevent sending more traffic to an already overloaded server, it can be sensible to reduce the default value to even 0.5. This would mean that instances with a queue longer than 50% of their maximum queue capacity would return HTTP 503 instead of HTTP 200 when their availability API is probed.

Preventing cluster overwhelm

From 3.8 on, there are some countermeasures built into Coordinators to prevent a cluster from being overwhelmed by too many concurrently executing requests.

This essentially works as follows: If a request is executed on a Coordinator but needs to wait for some operation on a DB-Server, the operating system thread executing the request can often postpone execution on the Coordinator, put the request to one side and do something else in the meantime. When the response from the DB-Server arrives, another worker thread will continue the work. This is a form of asynchronous implementation, which is great to achieve better thread utilization and enhance throughput.

On the other hand, this runs the risk that we start to work on new requests faster than we can finish off old ones. Before 3.8, this could actually happen, over time overwhelm the cluster and lead to nasty out of memory situations and other unwanted side effects. For example, it could lead to excessive latency for individual requests.

Therefore, beginning with Version 3.8, there is a limit as to how many requests coming from the low priority queue (most client requests are of this type), can be executed concurrently. The default value for this is 4 times as many as there are scheduler threads (see Server threads options), which is good for most workloads. Requests in excess of this will not be started but remain on the scheduler’s input queue (see Maximal queue size option).

The multiplier can be controlled with the following option:

--server.ongoing-low-priority-multiplier=<multiple>

This controls how many requests each Coordinator is allowed to execute concurrently, given as multiple of the maximum number of scheduler threads. The default is 4 and should be suitable for most workloads.

Very occasionally, 4 is already too much. You would notice this if the latency for individual requests is already too high because the system tries to execute too many of them at the same time (for example, if they fight for resources).

On the other hand, it is possible in other rare cases that throughput can be improved by increasing the value, if latency is not a big issue and all requests essentially spend their time waiting, so that a high concurrency does not hurt too much. Beware of your memory usage, though.

Storage engine

ArangoDB’s storage engine is based on RocksDB and the only available engine in ArangoDB v3.7 and above.

The legacy storage engine called MMFiles was removed.

One storage engine type is supported per server per installation. Live switching of storage engines on already installed systems isn’t supported. Configuring the wrong engine (not matching the previously used one) will result in the server refusing to start. You may however use auto to let ArangoDB choose the previously used one.

--server.storage-engine [auto|rocksdb]

Note that auto defaults to rocksdb.

Enable/disable authentication

--server.authentication

Setting this option to false will turn off authentication on the server side so all clients can execute any action without authorization and privilege checks.

The default value is true.

JWT Secrets

--server.jwt-secret-keyfile <file-with-secret>

ArangoDB will use JSON Web Tokens to authenticate requests. Using this option lets you specify a JWT secret stored in a file. The secret must be at most 64 bytes long.

In single server setups ArangoDB will generate a secret if none was specified.

In cluster deployments which have authentication enabled a secret must be set consistently across all cluster nodes so they can talk to each other.

ArangoDB also supports an option --server.jwt-secret <secret> to pass the secret directly (without a file), however this is discouraged for security reasons.

Multiple Secrets

Introduced in: v3.7.0

You may use multiple secrets, where the active secret is used to sign new JWT tokens and all other passive secrets are just used to validate incoming JWT tokens.

--server.jwt-secret-folder <folder-with-secrets>

The list of files in this folder is sorted alphabetically. The first is used as the active secret to sign new tokens. All other secrets are passively used during verification. Only one secret needs to verify a JWT token for it to be accepted.

Hot-Reload of JWT Secrets

Introduced in: v3.7.0

JWT secrets can be reloaded from disk without restarting the server or the nodes of a cluster deployment. It is supported for both, single keyfiles and secret folders (multiple secrets).

This may be used to roll out new JWT secrets throughout an ArangoDB cluster. See General HTTP Request Handling.

Enable/disable authentication for UNIX domain sockets

--server.authentication-unix-sockets value

Setting value to true will turn off authentication on the server side for requests coming in via UNIX domain sockets. With this flag enabled, clients located on the same host as the ArangoDB server can use UNIX domain sockets to connect to the server without authentication. Requests coming in by other means (e.g. TCP/IP) are not affected by this option.

The default value is false.

Note: this option is only available on platforms that support UNIX domain sockets.

Enable/disable authentication for system API requests only

--server.authentication-system-only boolean

Controls whether incoming requests need authentication only if they are directed to the ArangoDB’s internal APIs and features, located at /_api/, /_admin/ etc.

If the flag is set to true, then HTTP authentication is only required for requests going to URLs starting with /_, but not for other URLs. The flag can thus be used to expose a user-made API without HTTP authentication to the outside world, but to prevent the outside world from using the ArangoDB API and the admin interface without authentication. Note that checking the URL is performed after any database name prefix has been removed. That means when the actual URL called is /_db/_system/myapp/myaction, the URL /myapp/myaction will be used for authentication-system-only check.

The default is true.

Note that authentication still needs to be enabled for the server regularly in order for HTTP authentication to be forced for the ArangoDB API and the web interface. Setting only this flag is not enough.

You can control ArangoDB’s general authentication feature with the --server.authentication flag.

Enable authentication cache timeout

--server.authentication-timeout value

Sets the cache timeout to value (in seconds). This is only necessary if you use an external authentication system like LDAP.

Enable local authentication

--server.local-authentication value

If set to false only use the external authentication system. If true also use the local _users collections.

The default value is true.

Server threads

--server.minimal-threads number

--server.maximal-threads number

Specifies the number of threads that are spawned to handle requests.

The actual number of request processing threads is adjusted dynamically at runtime and will float between --server.minimal-threads and --server.maximal-threads.

--server.minimal-threads determines the minimum number of request processing threads the server will start and that will always be kept around. The default value is 2.

--server.maximal-threads determines the maximum number of request processing threads the server is allowed to start for request handling. If that number of threads is already running, arangod will not start further threads for request handling. The default value is max(32, 2 * available cores), so twice the number of CPU cores but at least 32 threads.

Toggling server statistics

--server.statistics

If this option’s value is false, then ArangoDB’s statistics gathering is turned off. Statistics gathering causes regular background CPU activity, memory usage and writes to the storage engine, so using this option to turn statistics off might relieve heavily-loaded instances a bit.

A side effect of setting this option to false is that no statistics will be shown in the dashboard of ArangoDB’s web interface, and that the REST API for server statistics at /_admin/statistics will return HTTP 404.

--server.statistics-history

If this option’s value is false, then ArangoDB’s statistics gathering is turned off. Statistics gathering causes regular background CPU activity, memory usage and writes to the storage engine, so using this option to turn statistics off might relieve heavily-loaded instances a bit.

When setting this option to false, no statistics will be shown in the dashboard of ArangoDB’s web interface, but the current statistics are available and can be queries using the REST API for server statistics at /_admin/statistics.

This is less intrusive than setting the --server.statistics option to false.

Data source flush synchronization

--server.flush-interval

ArangoDB will periodically ensure that all data sources (databases, views, etc.) have flushed all committed data to disk and write some checkpoint data to aid in future recovery. Increasing this value will result in fewer, larger write batches, while decreasing it will result in more, smaller writes. Setting the value too low can easily overwhelm the server, while setting the value too high may result in high memory usage and periodic slowdowns. Value is given in microseconds, with a typical range of 100000 (100ms) to 10000000 (10s) and a default of 1000000 (1s). Use caution when changing from the default.

Metrics API

--server.export-metrics-api

Enables or disables the Metrics HTTP API (both the deprecated and the new v2 one).