Use plugins

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Edge Microgateway v. 3.0.x

Audience

This topic is intended for Edge Microgateway operators who wish to use existing plugins that are installed with the microgateway. It also discusses the spike arrest and quota plugins in detail (both are included with the installation). If you're a developer who wants to develop new plugins, see Develop custom plugins.

What is an Edge Microgateway plugin?

A plugin is a Node.js module that adds functionality to Edge Microgateway. Plugin modules follow a consistent pattern and are stored in a location known to Edge Microgateway, enabling the microgateway to discover and load them automatically. Edge Microgateway includes several existing plugins and you can also create custom plugins, as explained in Develop custom plugins.

Existing plugins bundled with Edge Microgateway

Several existing plugins are provided with Edge Microgateway at installation. These include:

Where to find existing plugins

Existing plugins bundled with Edge Microgateway are located here, where [prefix] is the npm prefix directory. See Where is Edge Microgateway installed if you can't locate this directory.

[prefix]/lib/node_modules/edgemicro/node_modules/microgateway-plugins

Adding and configuring plugins

Follow this pattern to add and configure plugins:

1. Stop Edge Microgateway.
2. Open an Edge Microgateway configuration file. For details, see Making configuration changes for options.
3. Add the plugin to the plugins:sequence element of the config file, as follows. Plugins are executed in the order they appear in this list.

edgemicro:
  home: ../gateway
  port: 8000
  max_connections: -1
  max_connections_hard: -1
  logging:
     level: info
     dir: /var/tmp
     stats_log_interval: 60
  plugins:
     dir: ../plugins
     sequence:   
     - oauth
     - plugin-name

4. Configure the plugin. Some plugins have optional parameters that you can configure in the config file. For example, you can add the following stanza to configure the spike arrest plugin. See Using the spike arrest plugin for more information.

   edgemicro:
     home: ../gateway
     port: 8000
     max_connections: -1
     max_connections_hard: -1
     logging:
       level: info
       dir: /var/tmp
       stats_log_interval: 60
     plugins:
       dir: ../plugins
       sequence:
         - oauth
         - spikearrest
   spikearrest:
      timeUnit: minute
      allow: 10

5. Save the file.
6. Restart or reload Edge Microgateway, depending on which configuration file you edited.

Plugin-specific configuration

You can override the plugin parameters specified in the config file by creating a plugin-specific configuration in this directory:

[prefix]/lib/node_modules/edgemicro/node_modules/microgateway-plugins/config

where [prefix] is the npm prefix directory. See Where is Edge Microgateway installed if you can't locate this directory.

plugins/<plugin_name>/config/default.yaml. For example, you could put this block in plugins/spikearrest/config/default.yaml, and they will override any other config settings.

spikearrest:
   timeUnit: hour   
   allow: 10000   
   buffersize: 0

Using the spike arrest plugin

The spike arrest plugin protects against traffic spikes. It throttles the number of requests processed by an Edge Microgateway instance.

Adding the spike arrest plugin

See Adding and configuring plugins.

Sample configuration for spike arrest

edgemicro:
  home: ../gateway
  port: 8000
  max_connections: -1
  max_connections_hard: -1
  logging:
    level: info
    dir: /var/tmp
    stats_log_interval: 60
  plugins:
    dir: ../plugins
    sequence:
      - oauth
      - spikearrest
spikearrest:
   timeUnit: minute
   allow: 10
   bufferSize: 5

Configuration options for spike arrest

• timeUnit: How often the spike arrest execution window resets. Valid values are second or minute.
• allow: The maximum number of requests to allow during the timeUnit. See also If you're running multiple Edge Micro processes.
• bufferSize: (optional, default = 0) if bufferSize > 0, spike arrest stores this number of requests in a buffer. As soon as the next execution "window" occurs, the buffered requests will be processed first. See also Adding a buffer.

How does spike arrest work?

Think of spike arrest as a way to generally protect against traffic spikes rather than as a way to limit traffic to a specific number of requests. Your APIs and backend can handle a certain amount of traffic, and the spike arrest policy helps you smooth traffic to the general amounts you want.

The runtime spike arrest behavior differs from what you might expect to see from the literal per-minute or per-second values you enter.

For example, say you specify a rate of 30 requests per minute, like this:

spikearrest:
   timeUnit: minute
   allow: 30

In testing, you might think you could send 30 requests in 1 second, as long as they came within a minute. But that's not how the policy enforces the setting. If you think about it, 30 requests inside a 1-second period could be considered a mini spike in some environments.

What actually happens, then? To prevent spike-like behavior, spike arrest smooths the allowed traffic by dividing your settings into smaller intervals, as follows:

Per-minute rates

Per-minute rates get smoothed into requests allowed intervals of seconds. For example, 30 requests per minute gets smoothed like this:

60 seconds (1 minute) / 30 = 2-second intervals, or about 1 request allowed every 2 seconds. A second request inside of 2 seconds will fail. Also, a 31st request within a minute will fail.

Per-second rates

Per-second rates get smoothed into requests allowed in intervals of milliseconds. For example, 10 requests/second gets smoothed like this:

1000 milliseconds (1 second) / 10 = 100-millisecond intervals, or about 1 request allowed every 100 milliseconds . A second request inside of 100ms will fail. Also, an 11th request within a second will fail.

When the limit is exceeded

If the number of requests exceeds the limit within the specified time interval, spike arrest returns this error message with an HTTP 503 status:

{"error": "spike arrest policy violated"}

Adding a buffer

You have an option of adding a buffer to the policy. Let's say you set the buffer to 10. You'll see that the API does not return an error immediately when you exceed the spike arrest limit. Instead, requests are buffered (up to the number specified), and the buffered requests are processed as soon as the next appropriate execution window is available. The default bufferSize is 0.

If you're running multiple Edge Micro processes

The number of allowed requests depends on the number of Edge Micro worker processes that are running. Spike arrest calculates the allowable number of requests per worker process. By default, the number of Edge Micro processes equals the number of CPUs on the machine where Edge Micro is installed. However, you can configure the number of worker processes when you start Edge Micro using the --processes option on the start command. For example, if you want spike arrest to trigger at 100 requests in a given time period, and if you start Edge Microgateway with the option --processes 4, then set allow: 25 in the spike arrest config. In summary, the rule of thumb is to set the allow config parameter to the value "desired spike arrest count / number of processes".

Using the quota plugin

A quota specifies the number of request messages that an app is allowed to submit to an API over the course of an hour, day, week, or month. When an app reaches its quota limit, subsequent API calls are rejected. See also What's the difference between spike arrest and quota?.

Adding the quota plugin

See Adding and configuring plugins.

Product configuration in Apigee Edge

You configure quotas in the Apigee Edge UI where you configure API products. You need to know which product contains the microgateway-aware proxy that you want to limit with a quota. This product must be added to a developer app. When you make API calls that are authenticated using keys in the developer app, the quota will be applied to those API calls.

1. Log in to your Apigee Edge organization account.
2. In the Edge UI, open the product associated with the microgateway-aware proxy to which you want to apply the quota.
   1. In the UI, select Products from the Publish menu.
   2. Open the product containing the API to which you want to apply the quota.
   3. Click Edit.
   4. In the Quota field, specify the quota interval. For example, 100 requests every one minute. Or 50000 requests every 2 hours.
      
      

3. Click Save.
4. Be sure the product is added to a developer app. You'll need the keys from this app to make authenticated API calls.

Sample configuration for quota

edgemicro:
  home: ../gateway
  port: 8000
  max_connections: -1
  max_connections_hard: -1
  logging:
    level: info
    dir: /var/tmp
    stats_log_interval: 60
  plugins:
    dir: ../plugins
    sequence:
      - oauth
      - quota

Configuration options for quota

To configure the quota plugin, add the quotas element to your configuration file, as shown in the following example:

edgemicro:
  home: ../gateway
  port: 8000
  max_connections: -1
  max_connections_hard: -1
  logging:
    level: info
    dir: /var/tmp
    stats_log_interval: 60
  plugins:
    dir: ../plugins
    sequence:
      - oauth
      - quota
quotas:
  bufferSize:
    hour: 20000
    minute: 500
    month: 1
    default: 10000
  useDebugMpId: true
  failOpen: true
  useRedis: true
  redisHost: localhost
  redisPort: 6379
  redisDb: 1
...

edgemicro:
...
quotas:
  failOpen: true

edgemicro:
...
quotas:
  useDebugMpId: true
...

{
    "allowed": 20,
    "used": 3,
    "exceeded": 0,
    "available": 17,
    "expiryTime": 1570748640000,
    "timestamp": 1570748580323,
    "debugMpId": "6a12dd72-5c8a-4d39-b51d-2c64f953de6a"
}

Understanding quota scope

The quota count is scoped to an API product. If a developer app has multiple products, the quota is scoped to each one individually. To achieve this scope, Edge Microgateway creates a quota identifier that is a combination of "appName + productName".

Testing the quota plugin

When the quota is exceeded, an HTTP 403 status is returned to the client, along with the following message:

{"error": "exceeded quota"}

What's the difference between spike arrest and quota?

It’s important to choose the right tool for the job at hand. Quota policies configure the number of request messages that a client app is allowed to submit to an API over the course of an hour, day, week, or month. The quota policy enforces consumption limits on client apps by maintaining a distributed counter that tallies incoming requests.

Use a quota policy to enforce business contracts or SLAs with developers and partners, rather than for operational traffic management. For example, a quota might be used to limit traffic for a free service, while allowing full access for paying customers.

Use spike arrest to protect against sudden spikes in API traffic. Typically, spike arrest is used to head off possible DDoS or other malicious attacks.