.. _cp-production-recommendations: =========================== Running |ak| in Production =========================== This section describes the key considerations before going to production with |cp|. Hardware -------- If you’ve been following the normal development path, you’ve probably been playing with |ak-tm| on your laptop or on a small cluster of machines laying around. But when it comes time to deploying |ak| to production, there are a few recommendations that you should consider. Nothing is a hard-and-fast rule; |ak| is used for a wide range of use cases and on a bewildering array of machines. But these recommendations provide a good starting point based on the experiences of Confluent with production clusters. ------ Memory ------ |ak| relies heavily on the filesystem for storing and caching messages. All data is immediately written to a persistent log on the filesystem without necessarily flushing to disk. In effect this just means that it is transferred into the kernel's pagecache. A modern OS will happily divert all free memory to disk caching with little performance penalty when the memory is reclaimed. Furthermore, Kafka uses heap space very carefully and does not require setting heap sizes more than 6 GB. This will result in a file system cache of up to 28-30 GB on a 32 GB machine. You need sufficient memory to buffer active readers and writers. You can do a back-of-the-envelope estimate of memory needs by assuming you want to be able to buffer for 30 seconds and compute your memory need as ``write_throughput * 30``. A machine with 64 GB of RAM is a decent choice, but 32 GB machines are not uncommon. Less than 32 GB tends to be counterproductive (you end up needing many, many small machines). ---- CPUs ---- Most |ak| deployments tend to be rather light on CPU requirements. As such, the exact processor setup matters less than the other resources. Note that if :ref:`SSL ` is enabled, the CPU requirements can be significantly higher (the exact details depend on the CPU type and JVM implementation). You should choose a modern processor with multiple cores. Common clusters utilize 24 core machines. If you need to choose between faster CPUs or more cores, choose more cores. The extra concurrency that multiple cores offers will far outweigh a slightly faster clock speed. .. _cp-prod-disks: ----- Disks ----- You should use multiple drives to maximize throughput. Do not share the same drives used for |ak| data with application logs or other OS filesystem activity to ensure good latency. You can either combine these drives together into a single volume (RAID) or format and mount each drive as its own directory. Because |ak| has replication the redundancy provided by RAID can also be provided at the application level. This choice has several tradeoffs. If you configure multiple data directories, the broker places a new partition in the path with the least number of partitions currently stored. Each partition will be entirely in one of the data directories. If data is not well balanced among partitions, this can lead to load imbalance among disks. RAID can potentially do better at balancing load between disks (although it doesn't always seem to) because it balances load at a lower level. The primary downside of RAID is that it reduces the available disk space. Another potential benefit of RAID is the ability to tolerate disk failures. You should not use RAID 5 or RAID 6 because of the significant hit on write throughput and, to a lesser extent, the I/O cost of rebuilding the array when a disk fails (the rebuild cost applies to RAID, in general, but it is worst for RAID 6 and then RAID 5). You should use RAID 10 if the additional cost is acceptable. Otherwise, configure your |ak| server with multiple log directories, each directory mounted on a separate drive. Finally, you should avoid network-attached storage (NAS). NAS is often slower, displays larger latencies with a wider deviation in average latency, and is a single point of failure. ------- Network ------- A fast and reliable network is an essential performance component in a distributed system. Low latency ensures that nodes can communicate easily, while high bandwidth helps shard movement and recovery. Modern data-center networking (1 GbE, 10 GbE) is sufficient for the vast majority of clusters. ---------- Filesystem ---------- You should run |ak| on XFS or ext4. General Considerations ---------------------- In general, it is better to prefer medium-to-large boxes. Avoid small machines, because you don’t want to manage a cluster with a thousand nodes, and the overhead of simply running |ak| is more apparent on such small boxes. Avoid the large machines because they often lead to imbalanced resource usage. For example, all the memory is being used, but none of the CPU. They can also add logistical complexity if you have to run multiple nodes per machine. .. _vmware-opt: ------------------- VMware optimization ------------------- VMware `VMotion `__ and disk snapshotting features can help ensure the business continuity of workloads such as |cp| running atop vSphere. However, these features are known to impact the performance of |ak|. Confluent and VMWare recommend :ref:`enabling compression ` to help mitigate the performance impacts. For use cases where performance is more important than business continuity, Confluent recommends disabling VMotion and disk snapshotting for |cp|. JVM --- .. include:: ../includes/java-snippet.rst The recommended GC tuning (tested on a large deployment with JDK 1.8 u5) looks like this: .. codewithvars:: bash -Xms6g -Xmx6g -XX:MetaspaceSize=96m -XX:+UseG1GC -XX:MaxGCPauseMillis=20 -XX:InitiatingHeapOccupancyPercent=35 -XX:G1HeapRegionSize=16M -XX:MinMetaspaceFreeRatio=50 -XX:MaxMetaspaceFreeRatio=80 For reference, here are the stats on one of LinkedIn's busiest clusters (at peak): * 60 brokers * 50k partitions (replication factor 2) * 800k messages/sec in * 300 MBps inbound, 1 GBps + outbound The tuning looks fairly aggressive, but all of the brokers in that cluster have a 90% GC pause time of about 21ms, and they're doing less than 1 young GC per second. .. _cp-production-parameters: Production Configuration Options -------------------------------- The |ak| default settings should work in most cases, especially the performance-related settings and options, but there are some logistical configurations that should be changed for production depending on your cluster layout. --------------- General configs --------------- ``zookeeper.connect`` The list of |zk| hosts that the broker registers at. It is recommended that you configure this to all the hosts in your |zk| cluster * Type: string * Importance: high ``broker.id`` Integer ID that identifies a broker. Brokers in the same |ak| cluster must not have the same ID. * Type: int * Importance: high ``log.dirs`` The directories in which the |ak| log data is located. * Type: string * Default: "/tmp/kafka-logs" * Importance: high ``listeners`` Comma-separated list of URIs (including protocol) that the broker will listen on. Specify hostname as ``0.0.0.0`` to bind to all interfaces or leave it empty to bind to the default interface. An example is ``PLAINTEXT://myhost:9092``. * Type: string * Default: ``PLAINTEXT://host.name:port`` where the default for ``host.name`` is an empty string and the default for ``port`` is ``9092`` * Importance: high ``advertised.listeners`` Listeners to publish to |zk| for clients to use. In IaaS environments, this may need to be different from the interface to which the broker binds. If this is not set, the value for `listeners` will be used. * Type: string * Default: ``listeners`` * Importance: high .. _num-partitions: ``num.partitions`` The default number of log partitions for auto-created topics. You should increase this since it is better to over-partition a topic. Over-partitioning a topic leads to better data balancing and aids consumer parallelism. For keyed data, you should avoid changing the number of partitions in a topic. - Type: int - Default: 1 - Valid Values: [1,...] - Importance: medium - Dynamic Update Mode: read-only ------------------- Replication configs ------------------- ``default.replication.factor`` The default replication factor that applies to auto-created topics. You should set this to at least 2. * Type: int * Default: 1 * Importance: medium ``min.insync.replicas`` The minimum number of replicas in ISR needed to commit a produce request with ``required.acks=-1`` (or all). * Type: int * Default: 1 * Importance: medium ``unclean.leader.election.enable`` Indicates whether to enable replicas not in the ISR set to be elected as leader as a last resort, even though doing so may result in data loss. * Type: boolean * Default: false * Importance: medium .. _cp-production-file-descriptors: File Descriptors and mmap ------------------------- |ak| uses a very large number of files and a large number of sockets to communicate with the clients. All of this requires a relatively high number of available file descriptors. Many modern Linux distributions ship with only 1,024 file descriptors allowed per process. This is too low for |ak|. You should increase your file descriptor count to to at least 100,000. This process can be difficult and is highly dependent on your particular OS and distribution. Consult the documentation for your OS to determine how best to change the allowed file descriptor count. Here are some recommendations: To calculate the current mmap number, you can count the ``.index`` files in the |ak| data directory. The ``.index`` files represent the majority of the memory mapped files. Here is the procedure: #. Count the ``.index`` files using this command: :: find . -name '*index' | wc -l #. Set the ``vm.max_map_count`` for the session. This will calculate the current number of memory mapped files. The minimum value for mmap limit (``vm.max_map_count``) is the number of open files ulimit. .. important:: You should set ``vm.max_map_count`` sufficiently higher than the number of ``.index`` files to account for broker segment growth. :: sysctl -w vm.max_map_count=262144 #. Set the ``vm.max_map_count`` so that it will survive a reboot use this command: :: echo 'vm.max_map_count=262144' >> /etc/sysctl.conf sysctl -p Multi-node Configuration ------------------------ .. include:: includes/multi-node.rst