is etcd persistent

What is etcd etcd in Kubernetes?

etcd etcd is a highly available key-value store which Kubernetes uses for persistent storage of all of its objects like deployment, pod, service information. etcd has high access control, that it can be accessed only using API in master node. Nodes in the cluster other than master do not have access to etcd store.

Is etcd a good choice for CONFIG DATA?

I used etcd for all sorts of config data stuff, and did so for a long time. It's not a generic database, but rather, a key-value database. For data stores which need high-speed distributed access using a model which is based on retrieving values by key or range of keys, possibly with namespacing and granular access control, it's a great option.

What is the difference between Redis and etcd?

etcd cannot be stored in memory (ram) they can only be persisted in disk storage, whereas redis can be cached in ram and can also be persisted in disk. etcd does not have various data types. It is made to store only kubernetes objects. But redis and other key-value stores have data-type flexibility.

Is etcd a good key-value store?

Considering etcd as an key-value store, lets see the available nosql key-value data stores. Redis, memcached and memcacheDB are popular key-value stores. These are general-purpose distributed memory caching system often used to speed up dynamic database-driven websites by caching data and objects in memory.

What is etcd?

What are the two most commonly compared to etcd?

What is a.etcd file?

Is a distributed workload a small task?

Is ZooKeeper older than etcd?

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Is etcd consistent?

etcd is a consistent and durable key value store with mini-transaction support. The key value store is exposed through the KV APIs. etcd tries to ensure the strongest consistency and durability guarantees for a distributed system.

How is etcd strongly consistent?

etcd is a strongly consistent, distributed key-value store that provides a reliable way to store data that needs to be accessed by a distributed system or cluster of machines. It gracefully handles leader elections during network partitions and can tolerate machine failure, even in the leader node.

What type of database is etcd?

etcd is an open source distributed key-value store used to hold and manage the critical information that distributed systems need to keep running. Most notably, it manages the configuration data, state data, and metadata for Kubernetes, the popular container orchestration platform.

What happens if etcd goes down?

When a leader fails, the etcd cluster automatically elects a new leader. The election does not happen instantly once the leader fails. It takes about an election timeout to elect a new leader since the failure detection model is timeout based.

Can Kubernetes run without etcd?

Kubernetes uses etcd to store all its data – its configuration data, its state, and its metadata. Kubernetes is a distributed system, so it needs a distributed data store like etcd. etcd lets any of the nodes in the Kubernetes cluster read and write data.

Is etcd single threaded?

Everything in etcd is represented by a single-threaded state machine, which is great for simplicity and correctness, but that comes with performance limitations. etcd is used as the primary data store of applications like Kubernetes or CoreDNS.

Is etcd a NoSQL database?

There are more than 225 different NoSQL databases, including the more well known open source projects such as Cassandra, Redis, and Etcd, cloud-based versions such as Amazon Web Services DynamoDB, and proprietary products such as Oracle NoSQL.

Is application data stored in etcd?

etcd stores data (both key and value) as a binary array; the end user can apply whatever typing they want (often by storing values as JSON). And etcd uses a btree to index the keys, which is the same indexing that most any other DB uses on generic data.

Can Redis replace etcd?

Redis cannot replace etcd: etcd (like zookeeper and chubby) offer strong consistency, which Redis does not. These requirements are key for building things like a directory service (which is how CoreOS uses etcd).

Where is etcd data stored?

folder /var/lib/etcdBy default, etcd data is stored in folder /var/lib/etcd , which is most likely stored on the root file system. To avoid sharing the disk IOPS with other system components, it might be a good idea to migrate the etcd data directory to a dedicated file system to improve performance.

How do I know if etcd is running?

Check whether etcd container was started:Log in to your master node as a user with root permission.Run the following command to check etcd container status: docker ps | grep etcd. If etcd container was not started, run the following commands to get the logs: Get the etcd container ID: docker ps -a | grep etcd.

What is stored in etcd?

Etcd is an integral part of the Kubernetes control plane. Etcd stores Kubernetes cluster configuration and state data such as the number of pods, their state, namespace, etc. It also stores Kubernetes API objects and service discovery details.

Is ZooKeeper strongly consistent?

ZooKeeper provides "sequential consistency". This is weaker than linearizability but is still very strong, much stronger than "eventual consistency". ZooKeeper also provides a sync command.

Is etcd reliable?

etcd stores metadata in a consistent and fault-tolerant way. An etcd cluster is meant to provide key-value storage with best of class stability, reliability, scalability and performance.

How does etcd store data?

etcd stores data in a multiversion persistent key-value store. The persistent key-value store preserves the previous version of a key-value pair when its value is superseded with new data.

How does etcd replication work?

etcd uses a leader-based consensus protocol for consistent data replication and log execution. Cluster members elect a single leader, all other members become followers. The elected leader must periodically send heartbeats to its followers to maintain its leadership.

How etcd works with and without Kubernetes - Learnk8s

TL;DR: In this article, you will learn why Kubernetes uses etcd as a database by building (and breaking) a 3-node etcd cluster. If you've ever interacted with a Kubernetes cluster in any way, chances are it was powered by etcd under the hood.

Using etcd as primary store/database? - Stack Overflow

I used etcd for all sorts of config data stuff, and did so for a long time. It's not a generic database, but rather, a key-value database. For data stores which need high-speed distributed access using a model which is based on retrieving values by key or range of keys, possibly with namespacing and granular access control, it's a great option.

Could other factors prevent etcd from scaling with PMem?

Clusters are not only limited by single-node performance, but also by the time necessary to obtain consensus. Even if we make single nodes very fast, the cluster performance may still be bottlenecked by the network connecting the nodes.

Is resource utilization preventing etcd from scaling on PMem?

We started a small investigation into this by examining the resource utilization as the client load scales. The graph below shows how the CPU utilization of the etcd server (again, one node instead of a cluster) changed as the load increased. We used pidstat -C etcd -dul 5 to report the etcd CPU utilization and disk IO utilization. The graph shows that the CPU utilization was always below 1200%, showing that more than 16 CPUs didn’t help, and that it declined as the load increased. This indicates that some non-CPU bottleneck was slowing things down. The breakdown from pidstat also showed that more than 90% of the total CPU utilization was taken up in user code when the load was above 8,000 clients.

Etcd operator

Let’s start with etcd-operator. Don’t take me wrong, I think the operator concept is really good and etcd-operator can be a good way to manage an etcd cluster inside k8s, it’s just that, in its current shape, etcd-operator doesn’t meet the above requirement.

Statefulset

So another solution could be a stateful set with N replicas managing an etcd cluster like done with the above helm chart. What are the problems with it?

A possible solution

While I’d really like to have the etcd-operator features with a persistent etcd cluster, currently I have to rely other solutions.

Try it

You can find an example here: https://github.com/sgotti/k8s-persistent-etcd

Old solution

NOTE: this isn’t the best solution and was born with the (wrong) assumption that you won’t be able to specify a domain name in the etcd peerURLs in etcd 3.2. Since this isn’t true the single statefulset solution above is cleaner.

What is the purpose of a Kubernetes etcdis?

etcdis a highly available key-value store which Kubernetes uses for persistent storage of all of its objects like deployment, pod, serviceinformation.

What is Redis used for?

These are general-purpose distributed memory caching system often used to speed up dynamic database-driven websites by caching data and objects in memory.

Does etcd use SQL?

etcd stores data (both key and value) as a binary array; the end user can apply whatever typing they want (often by storing values as JSON). And etcd uses a btree to index the keys, which is the same indexing that most any other DB uses on generic data. It doesn't use SQL, I suppose, but "queries and searches" appropriate for data in a key-value DB are extremely fast in etcd.

Does ecsd give fast querying?

etcd guarantees only high availabilty, but does not give you the fast querying and indexing. All the nosql key-value stores are built with the goal of fast querying and searching.

Is etcd a replacement for NoSQL?

First, no. Etcd is not the next nosql replacement. But there are some sort of scenarios, where it can come in handy.

Why etcd?

Could the API server use a SQL database like MySQL or PostgreSQL to persist its data?

What happens if you give two arguments to etdctctl get?

If you give two arguments to etdctctl get, it will use a range query to return all key/value pairs in that range.

Does ecsd work in Kubernetes?

etcd works terrifically in thousands of Kubernetes clusters in the real world, but it might not be the best tool for all use cases.

What is it?

A persistent storage provider for Microsoft Orleans that scales on clusters. It is based on etcd.

Setup

The setup comparable to other orleans storage providers and is build using .NET Standard 2.0.3

Performance of etcd

Taken from an article from Core.OS, some performance comparisons are available on how etcd measures up agains Consul and Gatekeeper.

What is etcd?

etcd is an open source distributed key-value store used to hold and manage the critical information that distributed systems need to keep running. Most notably, it manages the configuration data, state data, and metadata for Kubernetes, the popular container orchestration platform.

What are the two most commonly compared to etcd?

The two most commonly compared to etcd are ZooKeeper and Consul.

What is a.etcd file?

The name “etcd” comes from a naming convention within the Linux directory structure: In UNIX, all system configuration files for a single system are contained in a folder called “/ etc;” “d” stands for “distributed.”

Is a distributed workload a small task?

It’s no small task to serve as the data backbone that keeps a distributed workload running. But etcd is built for the task, designed from the ground up for the following qualities:

Is ZooKeeper older than etcd?

ZooKeeper is older than etcd, and lessons learned from working with ZooKeeper influenced etcd’s design. As a result, etcd has some important capabilities that ZooKeeper does not. For example, unlike ZooKeeper, etcd can do the following: Allow for dynamic reconfiguration of cluster membership.

How Should We Test etcd Scalability?

Scaling Clients on A Server with Intel® Optane™ Persistent Memory

• We had access to a single 2-socket Cascade Lake system with PMem, and the system contained 1.5 TB (128 GB per DIMM) of Intel® Optane™ Persistent Memory distributed evenly among the 12 memory channels. We configured the system for app-direct mode and mounted a folder in the pmem0 device: sudo mount -t ext4 /dev/pmem0 /path/to/pmemDir/. The pmem0 dev...

See more on ibm.com

Is Resource Utilization Preventing etcd from Scaling on Pmem?

Could Other Factors Prevent etcd from Scaling with Pmem?

Conclusions

Acknowledgements