Adding developer guide

DEVELOPER_GUIDE.md

@@ -0,0 +1,228 @@
+- [Developer Guide](#developer-guide)
+  - [Getting Started](#getting-started)
+    - [Fork OpenSearch neural-search Repo](#fork-opensearch-neural-search-repo)
+    - [Install Prerequisites](#install-prerequisites)
+      - [JDK 11](#jdk-11)
+      - [Environment](#Environment)
+  - [Use an Editor](#use-an-editor)
+    - [IntelliJ IDEA](#intellij-idea)
+  - [Build](#build)
+  - [Run OpenSearch neural-search](#run-opensearch-neural-search)
+    - [Run Single-node Cluster Locally](#run-single-node-cluster-locally)
+    - [Run Multi-node Cluster Locally](#run-multi-node-cluster-locally)
+  - [Debugging](#debugging)
+  - [Supported configurations](#supported-configurations)
+  - [Submitting Changes](#submitting-changes)
+
+# Developer Guide
+
+So you want to contribute code to OpenSearch neural-search? Excellent! We're glad you're here. Here's what you need to do.
+
+## Getting Started
+
+### Fork OpenSearch neural-search Repo
+
+Fork [opensearch-project/OpenSearch neural-search](https://github.com/opensearch-project/neural-search) and clone locally.
+
+Example:
+```
+git clone https://github.com/[your username]/neural-search.git
+```
+
+### Install Prerequisites
+
+#### JDK 11
+
+OpenSearch builds using Java 11 at a minimum. This means you must have a JDK 11 installed with the environment variable 
+`JAVA_HOME` referencing the path to Java home for your JDK 11 installation, e.g. `JAVA_HOME=/usr/lib/jvm/jdk-11`.
+
+One easy way to get Java 11 on *nix is to use [sdkman](https://sdkman.io/).
+
+```bash
+curl -s "https://get.sdkman.io" | bash
+source ~/.sdkman/bin/sdkman-init.sh
+sdk install java 11.0.2-open
+sdk use java 11.0.2-open
+```
+
+JDK versions 14 and 17 were tested and are fully supported for local development.
+
+## Use an Editor
+
+### IntelliJ IDEA
+
+When importing into IntelliJ you will need to define an appropriate JDK. The convention is that **this SDK should be named "11"**, and the project import will detect it automatically. For more details on defining an SDK in IntelliJ please refer to [this documentation](https://www.jetbrains.com/help/idea/sdk.html#define-sdk). Note that SDK definitions are global, so you can add the JDK from any project, or after project import. Importing with a missing JDK will still work, IntelliJ will report a problem and will refuse to build until resolved.
+
+You can import the OpenSearch project into IntelliJ IDEA as follows.
+
+1. Select **File > Open**
+2. In the subsequent dialog navigate to the root `build.gradle` file
+3. In the subsequent dialog select **Open as Project**
+
+## Java Language Formatting Guidelines
+
+Taken from [OpenSearch's guidelines](https://github.com/opensearch-project/OpenSearch/blob/main/DEVELOPER_GUIDE.md):
+
+Java files in the OpenSearch codebase are formatted with the Eclipse JDT formatter, using the [Spotless Gradle](https://github.com/diffplug/spotless/tree/master/plugin-gradle) plugin. The formatting check can be run explicitly with:
+
+    ./gradlew spotlessJavaCheck
+
+The code can be formatted with:
+
+    ./gradlew spotlessApply
+
+Please follow these formatting guidelines:
+
+* Java indent is 4 spaces
+* Line width is 140 characters
+* Lines of code surrounded by `// tag::NAME` and `// end::NAME` comments are included in the documentation and should only be 76 characters wide not counting leading indentation. Such regions of code are not formatted automatically as it is not possible to change the line length rule of the formatter for part of a file. Please format such sections sympathetically with the rest of the code, while keeping lines to maximum length of 76 characters.
+* Wildcard imports (`import foo.bar.baz.*`) are forbidden and will cause the build to fail.
+* If *absolutely* necessary, you can disable formatting for regions of code with the `// tag::NAME` and `// end::NAME` directives, but note that these are intended for use in documentation, so please make it clear what you have done, and only do this where the benefit clearly outweighs the decrease in consistency.
+* Note that JavaDoc and block comments i.e. `/* ... */` are not formatted, but line comments i.e `// ...` are.
+* There is an implicit rule that negative boolean expressions should use the form `foo == false` instead of `!foo` for better readability of the code. While this isn't strictly enforced, it might get called out in PR reviews as something to change.
+
+## Build
+
+OpenSearch neural-search uses a [Gradle](https://docs.gradle.org/6.6.1/userguide/userguide.html) wrapper for its build. 
+Run `gradlew` on Unix systems.
+
+Build OpenSearch neural-search using `gradlew build` 
+
+```
+./gradlew build
+```
+
+## Run OpenSearch neural-search
+
+### Run Single-node Cluster Locally
+Run OpenSearch neural-search using `gradlew run`.
+
+```shell script
+./gradlew run
+```
+That will build OpenSearch and start it, writing its log above Gradle's status message. We log a lot of stuff on startup, specifically these lines tell you that plugin is ready.
+```
+[2023-10-24T16:26:24,789][INFO ][o.o.h.AbstractHttpServerTransport] [integTest-0] publish_address {127.0.0.1:9200}, bound_addresses {[::1]:9200}, {127.0.0.1:9200}
+[2023-10-24T16:26:24,793][INFO ][o.o.n.Node               ] [integTest-0] started
+```
+
+It's typically easier to wait until the console stops scrolling, and then run `curl` in another window to check if OpenSearch instance is running.
+
+```bash
+curl localhost:9200
+
+{
+  "name" : "integTest-0",
+  "cluster_name" : "integTest",
+  "cluster_uuid" : "XSMfCO3FR8CBzRnhG1AC7w",
+  "version" : {
+    "distribution" : "opensearch",
+    "number" : "3.0.0-SNAPSHOT",
+    "build_type" : "tar",
+    "build_hash" : "5bd413c588f48589c6fd6c4de4e87550271aecf8",
+    "build_date" : "2023-10-24T18:06:58.612820Z",
+    "build_snapshot" : true,
+    "lucene_version" : "9.8.0",
+    "minimum_wire_compatibility_version" : "2.12.0",
+    "minimum_index_compatibility_version" : "2.0.0"
+  },
+  "tagline" : "The OpenSearch Project: https://opensearch.org/"
+}
+```
+### Run Multi-node Cluster Locally
+
+It can be useful to test and debug on a multi-node cluster. In order to launch a 3 node cluster with the neural-search plugin installed, run the following command:
+
+```
+./gradlew run -PnumNodes=3
+```
+
+In order to run the integration tests with a 3 node cluster, run this command:
+
+```
+./gradlew :integTest -PnumNodes=3
+```
+
+Integration tests can be run with remote cluster. For that run the following command and replace host/port/cluster name values with ones for the target cluster:
+
+```
+./gradlew :integTestRemote -Dtests.rest.cluster=localhost:9200 -Dtests.cluster=localhost:9200 -Dtests.clustername="integTest-0" -Dhttps=false -PnumNodes=1
+```
+
+In case remote cluster is secured it's possible to pass username and password with the following command:
+
+```
+./gradlew :integTestRemote -Dtests.rest.cluster=localhost:9200 -Dtests.cluster=localhost:9200 -Dtests.clustername="integTest-0" -Dhttps=true -Duser=admin -Dpassword=admin
+```
+
+### Debugging
+
+Sometimes it is useful to attach a debugger to either the OpenSearch cluster or the integration test runner to see what's going on. For running unit tests, hit **Debug** from the IDE's gutter to debug the tests. For the OpenSearch cluster, first, make sure that the debugger is listening on port `5005`. Then, to debug the cluster code, run:
+
+```
+./gradlew :integTest -Dcluster.debug=1 # to start a cluster with debugger and run integ tests
+```
+
+OR
+
+```
+./gradlew run --debug-jvm # to just start a cluster that can be debugged
+```
+
+The OpenSearch server JVM will connect to a debugger attached to `localhost:5005` before starting. If there are multiple nodes, the servers will connect to debuggers listening on ports `5005, 5006, ...`
+
+To debug code running in an integration test (which exercises the server from a separate JVM), first, setup a remote debugger listening on port `8000`, and then run:
+
+```
+./gradlew :integTest -Dtest.debug=1
+```
+
+The test runner JVM will connect to a debugger attached to `localhost:8000` before running the tests.
+
+Additionally, it is possible to attach one debugger to the cluster JVM and another debugger to the test runner. First, make sure one debugger is listening on port `5005` and the other is listening on port `8000`. Then, run:
+```
+./gradlew :integTest -Dtest.debug=1 -Dcluster.debug=1
+```
+
+### Supported configurations
+
+By default, neural-search plugin supports `lucene` k-NN engine for local runs. Below is the sample request for creating of new index using this engine:
+
+```
+{
+    "settings": {
+        "index.knn": true,
+        "default_pipeline": "nlp-pipeline",
+        "number_of_shards": 2
+    },
+    "mappings": {
+        "properties": {
+            "passage_embedding": {
+                "type": "knn_vector",
+                "dimension": 768,
+                "method": {
+                    "name": "hnsw",
+                    "engine": "lucene"
+                }
+            },
+            "passage_text": {
+                "type": "text"
+            }
+        }
+    }
+}
+```
+
+The reason for this is that neural-search uses k-NN zip artifact from maven, and that artifact doesn't have native libraries. It's possible to install k-NN locally and build those native libraries (like Nmslib). For instructions on how to do this please check dev guide in [k-NN plugin repository.](https://github.com/opensearch-project/k-NN)
+
+## Submitting Changes
+
+See [CONTRIBUTING](CONTRIBUTING.md).
+
+## Backports
+
+The Github workflow in [`backport.yml`](.github/workflows/backport.yml) creates backport PRs automatically when the 
+original PR with an appropriate label `backport <backport-branch-name>` is merged to main with the backport workflow 
+run successfully on the PR. For example, if a PR on main needs to be backported to `2.x` branch, add a label 
+`backport 2.x` to the PR and make sure the backport workflow runs on the PR along with other checks. Once this PR is 
+merged to main, the workflow will create a backport PR to the `2.x` branch.