policy/frameworks/cluster/backend/zeromq/main.zeek
- Cluster::Backend::ZeroMQ
ZeroMQ cluster backend support.
Overview
For publish-subscribe functionality, one node in the Zeek cluster spawns a thread running a central broker listening on a XPUB and XSUB socket. These sockets are connected via zmq_proxy(). All other nodes connect to this central broker with their own XSUB and XPUB sockets, establishing a global many-to-many publish-subscribe system where each node sees subscriptions and messages from all other nodes in a Zeek cluster. ZeroMQ’s publish-subscribe pattern documentation may be a good starting point. Elsewhere in ZeroMQ’s documentation, the central broker is also called forwarder.
For remote logging functionality, the ZeroMQ pipeline pattern is used. All logger nodes listen on a PULL socket. Other nodes connect via PUSH sockets to all of the loggers. Concretely, remote logging functionality is not publish-subscribe, but instead leverages ZeroMQ’s built-in load-balancing functionality provided by PUSH and PULL sockets.
The ZeroMQ cluster backend technically allows to run a non-Zeek central broker (it only needs to offer XPUB and XSUB sockets). Further, it is possible to run non-Zeek logger nodes. All a logger node needs to do is open a ZeroMQ PULL socket and interpret the format used by Zeek nodes to send their log writes.
Overload Behavior
The ZeroMQ cluster backend by default drops outgoing and incoming events
when the Zeek cluster is overloaded. Dropping of outgoing events is governed
by the Cluster::Backend::ZeroMQ::xpub_sndhwm setting. This
is the High Water Mark (HWM) for the local XPUB socket’s queue. Once reached,
any outgoing events are dropped until there’s room in the socket’s queue again.
The metric zeek_cluster_zeromq_xpub_drops_total is incremented for every
dropped event.
For incoming events, the Cluster::Backend::ZeroMQ::onloop_queue_hwm
setting is used. Remote events received via the local XSUB socket are first
enqueued as raw event messages for processing on Zeek’s main event loop.
When this queue is full due to more remote events incoming than Zeek
can possibly process in an event loop iteration, incoming events are dropped
and the zeek_cluster_zeromq_onloop_drops_total metric is incremented.
Incoming log batches or subscription and unsubscription events are passed through the onloop queue, but the HWM does currently not apply to them. The assumption is that 1) these are not frequent and 2) more important than arbitrary publish-subscribe events.
To avoid dropping any events (e.g. for performance testing or offline PCAP
processing), the recommended strategy is to set both
Cluster::Backend::ZeroMQ::xpub_sndhwm and
Cluster::Backend::ZeroMQ::onloop_queue_hwm to 0,
disabling the HWM and dropping logic. It is up to the user to monitor CPU
and memory usage of individual nodes to avoid overloading and running into
out-of-memory situations.
As a Zeek operator, you should monitor zeek_cluster_zeromq_xpub_drops_total
and zeek_cluster_zeromq_onloop_drops_total. Any non-zero values for these
metrics indicate an overloaded Zeek cluster. See the the cluster telemetry
options Cluster::Telemetry::core_metrics and
Cluster::Telemetry::websocket_metrics for ways to get a better
understanding about the events published and received.
Encryption using the CURVE mechanism
When a Zeek cluster spans multiple systems on a shared and untrusted network, it’s strongly recommended to encrypt the network traffic between individual Zeek systems to avoid eavesdropping. ZeroMQ features built-in support for elliptic public-key encryption, offering confidentiality and authentication.
To enable it, generate keypairs for the server and client roles using
Cluster::Backend::ZeroMQ::generate_keypair and set the following
script-level variables:
Alternatively, set the environment variables:
ZEEK_CLUSTER_BACKEND_ZEROMQ_CURVE_CLIENT_PUBLICKEY
ZEEK_CLUSTER_BACKEND_ZEROMQ_CURVE_CLIENT_SECRETKEY
ZEEK_CLUSTER_BACKEND_ZEROMQ_CURVE_SERVER_PUBLICKEY
ZEEK_CLUSTER_BACKEND_ZEROMQ_CURVE_SERVER_SECRETKEY
To avoid confusion, either script-level or environment variable configuration should be used. Mixing the approaches will result in a fatal error at startup.
The central XPUB/XSUB sockets created by the proxy thread act as CURVE server. If you’re hosting the XPUB/XSUB sockets elsewhere or using a non-Zeek process, make sure to configure it with the proper secret key and provide the public key to the clients. The logger’s PULL socket uses the same secret key as the XPUB/XSUB sockets. This means logger nodes require access to the secret key even if the XPUB/XSUB component is external to Zeek. Additionally, the current implementation uses the client’s public key for authentication.
You may generate the keys as follows. Use to_json when there’s
a need to consume the key material elsewhere.
$ zeek -e ‘print to_json(Cluster::Backend::ZeroMQ::generate_keypair())’ {“public”:”l2A9cf[>&X7u=.GZFdHI=nz6QT6{$u^weYPEWJb/”,”secret”:”Z0eCkbrKkQBkO90Qb[j5mngd[0%Cl*bo}0<D+&vp”}
The encoding used is Z85.
All Zeek processes share and have access to the same credentials. Note that while the underlying protocol uses asymmetric cryptographic primitives, we use this more like shared symmetric encryption. Any external process with access to the server public key and the client secret and public key can connect to the central XPUB/XSUB sockets or any logger PULL socket.
Implementation Note
ZeroMQ’s ZAP protocol supports per-client authentication. We implement this lightly such that any client needs to possess the configured client secret and public key. Today, this means every node holds the client keys as by default the manager not only hosts the central XPUB/XSUB sockets, but also connects to them. It’s not clear if anything more is really useful. Advanced authentication or authorization concepts should probably be added to the WebSocket API instead.
- Namespace:
Cluster::Backend::ZeroMQ
- Imports:
Summary
Redefinable Options
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Vector of ZeroMQ endpoints to connect to for logging. |
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The central broker’s XPUB endpoint to connect to. |
Do not silently drop messages if high-water-mark is reached. |
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The central broker’s XSUB endpoint to connect to. |
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Client public key to use by Zeek processes connecting to the central XPUB/XSUB sockets and PULL sockets. |
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Client secret key to use by Zeek processes connecting to the central XPUB/XSUB sockets and PULL sockets. |
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Server public key to use for the central XPUB/XSUB sockets and the logger’s PULL sockets. |
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Server secret key to use for the central XPUB/XSUB sockets and logger PULL sockets. |
Bitmask to enable low-level stderr based debug printing. |
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Expiration for hello state. |
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The topic prefix used for internal ZeroMQ specific communication. |
Sets the ZMQ_IPV6 option on ZeroMQ contexts created by Zeek. |
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Configure the ZeroMQ’s sockets linger value. |
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PULL socket address to listen on for log messages. |
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XPUB listen endpoint for the central broker. |
Do not silently drop messages if high-water-mark is reached. |
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XSUB listen endpoint for the central broker. |
Configure ZeroMQ’s immediate setting on PUSH sockets |
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Kernel receive buffer size for log sockets. |
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Receive high water mark value for the log PULL sockets. |
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Kernel transmit buffer size for log sockets. |
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Send high water mark value for the log PUSH sockets. |
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Maximum number of incoming events queued for Zeek’s event loop. |
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Messages to receive before yielding. |
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How many IO threads to configure for the ZeroMQ context that acts as a central broker. |
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Toggle for running a central ZeroMQ XPUB-XSUB broker on this node. |
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Kernel transmit buffer size for the XPUB socket. |
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Send high water mark value for the XPUB socket. |
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Kernel receive buffer size for the XSUB socket. |
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Receive high water mark value for the XSUB socket. |
State Variables
The node topic prefix to use. |
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The node_id topic prefix to use. |
Redefinitions
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Events
Low-level event send to a node in response to their subscription. |
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Low-level event raised for ZeroMQ socket events. |
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Low-level event when a subscription is added. |
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Low-level event when a subscription vanishes. |
Detailed Interface
Redefinable Options
- Cluster::Backend::ZeroMQ::connect_log_endpoints
-
Vector of ZeroMQ endpoints to connect to for logging.
A node’s PUSH socket used for logging connects to each of the ZeroMQ endpoints listed in this vector.
- Cluster::Backend::ZeroMQ::connect_xpub_endpoint
-
The central broker’s XPUB endpoint to connect to.
A node connects with its XSUB socket to the XPUB socket of the central broker.
- Cluster::Backend::ZeroMQ::connect_xpub_nodrop
-
Do not silently drop messages if high-water-mark is reached.
Whether to configure
ZMQ_XPUB_NODROPon the XPUB socket connecting to the proxy to detect when sending a message fails due to reaching the high-water-mark. If you set this to F, then the XPUB drops metric will stop working as sending on the XPUB socket will always succeed. Unless you’re developing on the ZeroMQ cluster backend, keep this set to T.See ZeroMQ’s ZMQ_XPUB_NODROP documentation for more details.
- Cluster::Backend::ZeroMQ::connect_xsub_endpoint
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The central broker’s XSUB endpoint to connect to.
A node connects with its XPUB socket to the XSUB socket of the central broker.
- Cluster::Backend::ZeroMQ::curve_client_publickey
-
Client public key to use by Zeek processes connecting to the central XPUB/XSUB sockets and PULL sockets.
- Cluster::Backend::ZeroMQ::curve_client_secretkey
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Client secret key to use by Zeek processes connecting to the central XPUB/XSUB sockets and PULL sockets.
- Cluster::Backend::ZeroMQ::curve_server_publickey
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Server public key to use for the central XPUB/XSUB sockets and the logger’s PULL sockets.
This key is used by Zeek processes for the connection to the central XPUB/XSUB sockets and individual logger PULL sockets as the public CURVE server key.
- Cluster::Backend::ZeroMQ::curve_server_secretkey
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Server secret key to use for the central XPUB/XSUB sockets and logger PULL sockets.
- Cluster::Backend::ZeroMQ::debug_flags
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Bitmask to enable low-level stderr based debug printing.
poll: 1 (produce verbose zmq::poll() output) thread: 2 (produce thread related output)
Or values from the above list together and set debug_flags to the result. E.g. use 7 to select 4, 2 and 1. Only use this in development if something seems off. The thread used internally will produce output on stderr.
- Cluster::Backend::ZeroMQ::hello_expiration
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Expiration for hello state.
How long to wait before expiring information about subscriptions and hello messages from other nodes. These expirations trigger reporter warnings.
- Cluster::Backend::ZeroMQ::internal_topic_prefix
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The topic prefix used for internal ZeroMQ specific communication.
This is used for the “ready to publish callback” topics.
Zeek creates a short-lived subscription for a auto-generated topic name with this prefix and waits for it to be confirmed on its XPUB socket. Once this happens, the XPUB socket should’ve also received all other active subscriptions of other nodes in a cluster from the central XPUB/XSUB proxy and therefore can be deemed ready for publish operations.
- Cluster::Backend::ZeroMQ::ipv6
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Sets the ZMQ_IPV6 option on ZeroMQ contexts created by Zeek.
By default, IPv6 support on the ZeroMQ context is disabled. If you’re using IPv6 addresses for any of the endpoint options, or you’re using Zeek in a dual-stack environment and want to listen on IPv6 and IPv4 addresses at the same time, set this option to
T. If you’re deploying Zeek using ZeekControl, this will happen automatically.See ZeroMQ’s ZMQ_IPV6 documentation for more details.
- Cluster::Backend::ZeroMQ::linger_ms
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Configure the ZeroMQ’s sockets linger value.
The default used by libzmq is 30 seconds (30 000) which is very long when loggers vanish before workers during a shutdown, so we reduce this to 500 milliseconds by default.
A value of
-1configures blocking forever, while0would immediately discard any pending messages.See ZeroMQ’s ZMQ_LINGER documentation for more details.
- Cluster::Backend::ZeroMQ::listen_log_endpoint
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PULL socket address to listen on for log messages.
If empty, don’t listen for log messages, otherwise a ZeroMQ address to bind to. E.g.,
tcp://127.0.0.1:5555.
- Cluster::Backend::ZeroMQ::listen_xpub_endpoint
-
XPUB listen endpoint for the central broker.
This setting is used for the XPUB socket of the central broker started when
Cluster::Backend::ZeroMQ::run_proxy_threadisT.
- Cluster::Backend::ZeroMQ::listen_xpub_nodrop
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Do not silently drop messages if high-water-mark is reached.
Whether to configure
ZMQ_XPUB_NODROPon the XPUB socket to detect when sending a message fails due to reaching the high-water-mark.This setting applies to the XPUB/XSUB broker started when
Cluster::Backend::ZeroMQ::run_proxy_threadisT.See ZeroMQ’s ZMQ_XPUB_NODROP documentation for more details.
- Cluster::Backend::ZeroMQ::listen_xsub_endpoint
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XSUB listen endpoint for the central broker.
This setting is used for the XSUB socket of the central broker started when
Cluster::Backend::ZeroMQ::run_proxy_threadisT.
- Cluster::Backend::ZeroMQ::log_immediate
-
Configure ZeroMQ’s immediate setting on PUSH sockets
Setting this to
Twill queue log writes only to completed connections. By default, log writes are queued to all potential endpoints listed inCluster::Backend::ZeroMQ::connect_log_endpoints.See ZeroMQ’s ZMQ_IMMEDIATE documentation for more details.
- Cluster::Backend::ZeroMQ::log_rcvbuf
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Kernel receive buffer size for log sockets.
Using -1 will use the kernel’s default.
See ZeroMQ’s ZMQ_RCVBUF documentation for more details.
- Cluster::Backend::ZeroMQ::log_rcvhwm
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Receive high water mark value for the log PULL sockets.
If reached, Zeek workers will block or drop messages.
See ZeroMQ’s ZMQ_RCVHWM documentation for more details.
TODO: Make action configurable (block vs drop)
- Cluster::Backend::ZeroMQ::log_sndbuf
-
Kernel transmit buffer size for log sockets.
Using -1 will use the kernel’s default.
See ZeroMQ’s ZMQ_SNDBUF documentation.
- Cluster::Backend::ZeroMQ::log_sndhwm
-
Send high water mark value for the log PUSH sockets.
If reached, Zeek nodes will block or drop messages.
See ZeroMQ’s ZMQ_SNDHWM documentation for more details.
TODO: Make action configurable (block vs drop)
- Cluster::Backend::ZeroMQ::onloop_queue_hwm
-
Maximum number of incoming events queued for Zeek’s event loop.
This constant defines the maximum number of remote events queued by the ZeroMQ cluster backend for Zeek’s event loop to drain in one go. If you set this value to 0 (unlimited), consider closely CPU and memory usage of cluster nodes as high remote event rates may starve packet processing.
If more events are received than can fit the queue, new events will be dropped and the
zeek_cluster_zeromq_onloop_drops_totalmetric incremented.
- Cluster::Backend::ZeroMQ::poll_max_messages
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Messages to receive before yielding.
Yield from the receive loop when this many messages have been received from one of the used sockets.
- Cluster::Backend::ZeroMQ::proxy_io_threads
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How many IO threads to configure for the ZeroMQ context that acts as a central broker. See ZeroMQ’s ZMQ_IO_THREADS documentation and the I/O threads section in the ZeroMQ guide for details.
- Cluster::Backend::ZeroMQ::run_proxy_thread
- Type:
- Attributes:
- Default:
F- Redefinition:
from policy/frameworks/cluster/backend/zeromq/main.zeek
=:Cluster::local_node_type() == Cluster::MANAGER
- Redefinition:
from policy/frameworks/cluster/websocket/server.zeek
=:``T``
Toggle for running a central ZeroMQ XPUB-XSUB broker on this node.
If set to
T,Cluster::Backend::ZeroMQ::spawn_zmq_proxy_threadis called duringzeek_init. The node will listen onCluster::Backend::ZeroMQ::listen_xsub_endpointandCluster::Backend::ZeroMQ::listen_xpub_endpointand forward subscriptions and messages between nodes.By default, this is set to
Ton the manager andFelsewhere.
- Cluster::Backend::ZeroMQ::xpub_sndbuf
-
Kernel transmit buffer size for the XPUB socket.
Using -1 will use the kernel’s default.
See ZeroMQ’s ZMQ_SNDBUF documentation for more details.
- Cluster::Backend::ZeroMQ::xpub_sndhwm
-
Send high water mark value for the XPUB socket.
Events published when the XPUB queue is full will be dropped and the
zeek_cluster_zeromq_xpub_drops_totalmetric incremented.See ZeroMQ’s ZMQ_SNDHWM documentation for more details.
- Cluster::Backend::ZeroMQ::xsub_rcvbuf
-
Kernel receive buffer size for the XSUB socket.
Using -1 will use the kernel’s default.
See ZeroMQ’s ZMQ_RCVBUF documentation for more details.
- Cluster::Backend::ZeroMQ::xsub_rcvhwm
-
Receive high water mark value for the XSUB socket.
If reached, the Zeek node will start reporting back pressure to the central XPUB socket.
See ZeroMQ’s ZMQ_RCVHWM documentation for more details.
State Variables
- Cluster::Backend::ZeroMQ::node_topic_prefix
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The node topic prefix to use.
- Cluster::Backend::ZeroMQ::nodeid_topic_prefix
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The node_id topic prefix to use.
Events
- Cluster::Backend::ZeroMQ::hello
-
Low-level event send to a node in response to their subscription.
- Parameters:
name – The sending node’s name in
Cluster::nodes.id – The sending node’s identifier, as generated by
Cluster::node_id.
- Cluster::Backend::ZeroMQ::monitoring_event
-
Low-level event raised for ZeroMQ socket events.
See
zmq_socket_monitor()and theZMQ_EVENT_*constants inzmq.hfor possible values ofnumberandvalue.- Parameters:
number – The event number.
value – The event value.
address – The socket address of the event.
- Cluster::Backend::ZeroMQ::subscription
-
Low-level event when a subscription is added.
Every node observes all subscriptions from other nodes in a cluster through its XPUB socket. Whenever a new subscription topic is added, this event is raised with the topic.
- Parameters:
topic – The topic.
- Cluster::Backend::ZeroMQ::unsubscription
-
Low-level event when a subscription vanishes.
Every node observes all subscriptions from other nodes in a cluster through its XPUB socket. Whenever a subscription is removed from the local XPUB socket, this event is raised with the topic set to the removed subscription.
- Parameters:
topic – The topic.