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Discovery

This service provides a REST interface for querying for the list of hosts that belong to a given service in microservice infrastructure. Host information is written to and read from backend store (DynamoDB by default). This project relies on the following libraries:

Flask (web-framework)
Flask-Cache (for caching and reusing results for GET requests)
Pynamodb (for reading/writing DynamoDB data)

Also check requirements.txt for other dependencies.

Discovery service settings

Discovery service settings are controlled by environment variables.

HOST_TTL
- If the last heartbeat was not performed in the last HOST_TTL seconds, discovery service will remove host from backend storage. Default value is 600 (10 minutes).
CACHE_TTL
- Flask cache expiration in seconds, discovery calls BACKEND_STORAGE to fill the cache. This cache is used for hosts retrieval by service or service repo. Default value is 30 seconds.
BACKEND_STORAGE
- Type of the backend storage used in discovery service. Supported values are: DynamoDB, InMemory, InFile. By default DynamoDB backend is used.
CACHE_TYPE
- Supported values 'simple' or 'null'. Default value is 'null' which effectively turn flask caching off.
APPLICATION_DIR
- Application directory.
APPLICATION_ENV
- Environment discovery service runs in, e.g., development or production. Default value is development.
DEBUG
- If debug mode is used. Default value is true.
LOG_LEVEL
- Set logging level. Default value is DEBUG.
PORT
- Port flask app using. Default value is 8080.
DYNAMODB_TABLE_HOSTS
- Used only in case of DynamoDB backend.
DYNAMODB_URL
- Used only for development in case of DynamoDB backend running locally.
DYNAMODB_CREATE_TABLES_IN_APP
- Used for creating DynamoDB table, useful only in case DynamoDB backend storage used.

API

GET /v1/registration/:service

Returns metadata for the given :service.

service
- (required, string) name of the service metadata is queried for.

On successful response, response body will be in the following JSON format:

{
    "env": "...",
    "hosts": [],
    "service": "..."
}

env
- (required, string) environment discovery service runs in, e.g., development or production.
hosts
- (required, object) list of non expired hosts (hosts that last checked in to discovery service in the last HOST_TTL period). Each host is in the following JSON format:
```
{
    "ip_address": "...",
    "last_check_in": "...",
    "port": 9211,
    "revision": "...",
    "service": "...",
    "service_repo_name": "...",
    "tags": {}
}
```
- ip_address
  - (required, string) ip address of the host.
- last_check_in
  - (required, string) heartbeat timestamp converted to string, last time host registered with discovery service.
- port
  - (required, integer) port on which the host expects connections, Envoy will connect to this port.
- revision
  - (required, string) service SHA running on the host.
- service
  - (required, string) service name.
- service_repo_name
  - (required, string) service repo, used for selecting hosts based on the service_repo (can be empty if not set).
- tags
  - (required, object) see tags here.
service
- (required, string) service name.

GET /v1/registration/repo/:service_repo_name

Returns list of non expired hosts for :service_repo_name (query based on secondary index, for example, DynamoDB GSI). Format is the same as query based on service.

POST /v1/registration/:service

Registers a host with a service. Response body does not contain any data.

service
- (required, string) Service for which operation is performed.

Request params:

ip
- (required, string) ip address of the host.
service_repo_name
- (optional, string) service repository name, can be used for quick search.
port
- (required, integer) port on which the host expects connections, Envoy will connect to this port.
revision
- (required, string) SHA of the revision the service is currently running.
tags
- (required, object) JSON in the following format.

DELETE /v1/registration/:service/:ip_address

Deletes the host for the given service with ip_address. Returns response code 400 if no service/ip_address entity exists.

service
- (required, string) name of the service metadata is queried for.
ip
- (required, string) ip address of the host.

POST /v1/loadbalancing/:service/:ip_address

Updates the weight of hosts for load balancing purposes.

service
- (required, string) Service name for which weight is updated.
ip_address
- (optional, string) IP address of the host for which weight is updated. If not given, all hosts for the given service will have their weights updated.

Request params:

load_balancing_weight
- (required, integer) Host weight, an integer between 1 and 100.

Tags JSON

  {
     "az": "...",
     "region": "...",
     "instance_id": "...",
     "canary": false,
     "load_balancing_weight": 1
  }

az
- (required, string) AWS availability zone that the host is running in. You can provide arbitrary but the same value for all hosts if zone aware stats/routing is not required. If you use non AWS backend storage currently you have to provide az anyway, you can use some fixed predefined value for all hosts.
region
- (required, string) AWS region that the host is running in.
instance_id
- (required, string) AWS instance_id of the host.
canary
- (optional, boolean) Set to true if host is a canary instance, used by Envoy.
load_balancing_weight:
- (optional, integer) Load balancing weight is used by Envoy for weighted routing. Values must be an integer between 1 and 100.

Main Classes

app/routes/api.py
defines the HTTP routes for service registration
app/resources/api.py
the entry point for service registration GETs and POSTs
app/services/host.py
contains the business logic (e.g. caching, input validation, etc) for service registration GETS and POSTs
app/models/host.py
The pynamo model for service registration information for a host

Unit Testing

Note currently it's not working on public repository without tweaking (there is an opened issue for this) To run all unit tests, run make test_unit.

lyft/discovery

lyft

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