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Spring etcd Example

This is an example of using etcd v3.0 with Spring Boot. The application uses jetcd v0.0.1, a Java client for etcd, to communicate with the database.

Introduction to etcd

etcd is a distributed key-value store. It is written in Go and uses Raft protocol to communicate between different nodes in the cluster. Raft is a protocol for implementing distributed consensus.

etcd has a well-defined API to interact with clients. It uses gRPC protocol to communicate with clients. As with any RPC (Remote Procedure Call) application, a gRPC client invokes methods remotely on services defined in a server. gRPC uses protocol buffers for serializing data across the wire.

etcd is widely used in applications such as Kubernetes.

etcd Installation

You can download the the prebuilt etcd binary here. Binaries are available for OSX, Linux, Windows, etc.

Once you download the zip (or tar) file, uncompress it and save it in a folder of your choice. In my example, the files are saved in a folder named etcd-v3.3.0.

Running etcd

To start th etcd server, naivigate to the folder where you saved the downloaded binaries earlier. In this example, the saved folder is etcd-v3.3.0.

Type the following command to start a single-member cluster of etcd,

etcd

It will bring up the etcd server listening on port 2379 for client communication and on port 2380 for server-to-server communication.

$ ./etcd
2017-12-28 10:39:28.289152 I | etcdmain: etcd Version: 3.3.0
2017-12-28 10:39:28.289235 I | etcdmain: Git SHA: f7a395f
2017-12-28 10:39:28.289253 I | etcdmain: Go Version: go1.9.2
2017-12-28 10:39:28.289258 I | etcdmain: Go OS/Arch: darwin/amd64
2017-12-28 10:39:28.289264 I | etcdmain: setting maximum number of CPUs to 8, total number of available CPUs is 8
2017-12-28 10:39:28.289276 N | etcdmain: failed to detect default host (default host not supported on darwin_amd64)
2017-12-28 10:39:28.289287 W | etcdmain: no data-dir provided, using default data-dir ./default.etcd
2017-12-28 10:39:28.289355 N | etcdmain: the server is already initialized as member before, starting as etcd member...
2017-12-28 10:39:28.289689 I | embed: listening for peers on http://localhost:2380
2017-12-28 10:39:28.289847 I | embed: listening for client requests on localhost:2379
2017-12-28 10:39:28.290816 I | etcdserver: name = default
2017-12-28 10:39:28.290827 I | etcdserver: data dir = default.etcd
2017-12-28 10:39:28.290834 I | etcdserver: member dir = default.etcd/member
2017-12-28 10:39:28.290842 I | etcdserver: heartbeat = 100ms
2017-12-28 10:39:28.290848 I | etcdserver: election = 1000ms
2017-12-28 10:39:28.290853 I | etcdserver: snapshot count = 100000
2017-12-28 10:39:28.290862 I | etcdserver: advertise client URLs = http://localhost:2379
2017-12-28 10:39:28.468847 I | etcdserver: restarting member 8e9e05c52164694d in cluster cdf818194e3a8c32 at commit index 17
2017-12-28 10:39:28.468922 I | raft: 8e9e05c52164694d became follower at term 4
2017-12-28 10:39:28.468942 I | raft: newRaft 8e9e05c52164694d [peers: [], term: 4, commit: 17, applied: 0, lastindex: 17, lastterm: 4]
2017-12-28 10:39:28.476762 W | auth: simple token is not cryptographically signed
2017-12-28 10:39:28.477581 I | etcdserver: starting server... [version: 3.3.0, cluster version: to_be_decided]
2017-12-28 10:39:28.477714 E | etcdserver: cannot monitor file descriptor usage (cannot get FDUsage on darwin)
2017-12-28 10:39:28.478147 I | etcdserver/membership: added member 8e9e05c52164694d [http://localhost:2380] to cluster cdf818194e3a8c32
2017-12-28 10:39:28.478265 N | etcdserver/membership: set the initial cluster version to 3.3
2017-12-28 10:39:28.478321 I | etcdserver/api: enabled capabilities for version 3.3
2017-12-28 10:39:29.070709 I | raft: 8e9e05c52164694d is starting a new election at term 4
2017-12-28 10:39:29.070760 I | raft: 8e9e05c52164694d became candidate at term 5
2017-12-28 10:39:29.070793 I | raft: 8e9e05c52164694d received MsgVoteResp from 8e9e05c52164694d at term 5
2017-12-28 10:39:29.070815 I | raft: 8e9e05c52164694d became leader at term 5
2017-12-28 10:39:29.070838 I | raft: raft.node: 8e9e05c52164694d elected leader 8e9e05c52164694d at term 5
2017-12-28 10:39:29.071171 I | embed: ready to serve client requests
2017-12-28 10:39:29.071203 I | etcdserver: published {Name:default ClientURLs:[http://localhost:2379]} to cluster cdf818194e3a8c32
2017-12-28 10:39:29.072107 N | embed: serving insecure client requests on 127.0.0.1:2379, this is strongly discouraged!

Running etcdctl

etcdctl is a command line client for etcd. Before using etcdctl, set the environment variable,ETCDCTL_API, to use version 3 API of etcd.

export ETCDCTL_API=3

The etcdctl tool is located in the same folder as etcd.

PUT Command

Use PUT command to create a new key-value pair. Use the following coomand to create a key named foo with a value named bar.

./etcdctl put foo bar

It should print out OK if everything goes well.

GET Command

Use GET command to retrieve the value,

./etcdctl get foo

The output should be,

foo
bar

There shouldn't be any output if no key is found.

To retrieve all keys, provide an empty string as key,

 ./etcdctl get "" --prefix=true

Here is the output,

bc168652-9f13-4866-bab2-158e27fe19f5
{"id":"bc168652-9f13-4866-bab2-158e27fe19f5","title":"Indra-1","author":"Indra Basak"}
c5413351-c292-4fdf-80ae-876cf8e9e8fc
{"id":"c5413351-c292-4fdf-80ae-876cf8e9e8fc","title":"indra's book","author":"indra"}

To retrieve all keys with prefix Books, use the following command,

./etcdctl get "Books" --prefix=true

Here is the output,

Books32a4c9fb-dd79-4a15-a139-51317da3f2e3
{"id":"32a4c9fb-dd79-4a15-a139-51317da3f2e3","title":"Indra's Chronicle","author":"Indra Basak"}
Books577c6ba4-303e-4065-90f1-bdf8ad255911
{"id":"577c6ba4-303e-4065-90f1-bdf8ad255911","title":"hello there","author":"Indra Basak"}
Booksa3e546bd-85f1-44bf-9edb-bbe7ee293a0a
{"id":"a3e546bd-85f1-44bf-9edb-bbe7ee293a0a","title":"hello there 2","author":"Indra Basak"}

etcd Client Configuration

You can configure the etcd connection in this example Spring Boot application by specifying the ectd server URIs in the application.yml. Currently, the application expects the etcd server to be available at http://localhost:2379.

etcd:
  uris: http://localhost:2379

You also can specify multiple etcd servers as acomma separated list,

etcd:
  uris: http://host1:2379, http://host2:2380

Build

To build the JAR, execute the following command from the parent directory:

mvn clean install

Run

Run the executable jar from the command to start the application,

java -jar target/spring-etcd-example-1.0.0.jar

You should have the following output once the application starts up successfully,

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.5.8.RELEASE)

2017-12-28 17:20:32.659  INFO 13438 --- [           main] com.basaki.Application                   : Starting Application on ibasa-mb-46063.local with PID 13438 (/Users/spring-etcd-example/target/spring-etcd-example-1.0.0.jar started by indra.basak in /Users/spring-etcd-example)
2017-12-28 17:20:32.663  INFO 13438 --- [           main] com.basaki.Application                   : No active profile set, falling back to default profiles: default
2017-12-28 17:20:32.733  INFO 13438 --- [           main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@2f333739: startup date [Thu Dec 28 17:20:32 PST 2017]; root of context hierarchy
...
2017-12-28 17:20:35.998  INFO 13438 --- [           main] d.s.w.p.DocumentationPluginsBootstrapper : Found 1 custom documentation plugin(s)
2017-12-28 17:20:36.060  INFO 13438 --- [           main] s.d.s.w.s.ApiListingReferenceScanner     : Scanning for api listing references
2017-12-28 17:20:36.394  INFO 13438 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)
2017-12-28 17:20:36.399  INFO 13438 --- [           main] com.basaki.Application                   : Started Application in 4.388 seconds (JVM running for 4.883)

Usage

The application starts up at port 8080. You can access the swagger UI at http://localhost:8080/swagger-ui.html. From the UI, you can create, retrieve, and delete book entities.