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aws-api

aws-api provides programmatic access to AWS services from Clojure programs.

Docs

Rationale

AWS APIs are data-oriented in both the "send data, get data back" sense, and the fact that all of the operations and data structures for every service are, themselves, described in data which can be used to generate mechanical transformations from application data to wire data and back. This is exactly what we want from a Clojure API.

Using the AWS Java SDK directly via interop requires knowledge of OO hierarchies of data classes, and while the existing Clojure wrappers hide much of this from you, they don't hide it from your process.

aws-api is an idiomatic, data-oriented Clojure library for invoking AWS APIs. While the library offers some helper and documentation functions you'll use at development time, the only functions you ever need at runtime are client, which creates a client for a given service and invoke, which invokes an operation on the service. invoke takes a map and returns a map, and works the same way for every operation on every service.

Approach

AWS APIs are described in data which specifies operations, inputs, and outputs. aws-api uses the same data descriptions to expose a data-oriented interface, using service descriptions, documentation, and specs which are generated from the source descriptions.

Most AWS SDKs have their own copies of these data descriptions in their github repos. We use aws-sdk-js as the source for these, and release separate artifacts for each api. The api descriptors include the AWS api-version in their filenames (and in their data). For example you'll see both of the following files listed:

dynamodb-2011-12-05.normal.json
dynamodb-2012-08-10.normal.json

Whenever we release com.cognitect.aws/dynamodb, we look for the descriptor with the most recent API version. If aws-sdk-js-v2.351.0 contains an update to dynamodb-2012-08-10.normal.json, or a new dynamodb descriptor with a more recent api-version, we'll make a release whose version number includes the 2.351.0 from the version of aws-sdk-js.

We also include the revision of our generator in the version. For example, com.cognitect.aws/dynamo-db-653.2.351.0 indicates revision 653 of the generator, and tag v2.351.0 of aws-sdk-js.

  • See Versioning for more about how we version releases.
  • See latest releases for a list of the latest releases of api, endpoints, and all supported services.

Usage

dependencies

To use aws-api in your application, you depend on com.cognitect.aws/api, com.cognitect.aws/endpoints and the service(s) of your choice, e.g. com.cognitect.aws/s3.

To use the s3 api, for example, add the following to deps.edn:

{:deps {com.cognitect.aws/api       {:mvn/version "0.8.692"}
        com.cognitect.aws/endpoints {:mvn/version "1.1.12.701"}
        com.cognitect.aws/s3        {:mvn/version "868.2.1580.0"}}}
  • See latest releases for a listing of the latest releases of api, endpoints, and all supported services.

explore!

Fire up a REPL using that deps.edn, and then you can do things like this:

(require '[cognitect.aws.client.api :as aws])

Create a client:

(def s3 (aws/client {:api :s3}))

Ask what ops your client can perform:

(aws/ops s3)

Look up docs for an operation:

(aws/doc s3 :CreateBucket)

Tell the client to let you know when you get the args wrong:

(aws/validate-requests s3 true)

Do stuff:

(aws/invoke s3 {:op :ListBuckets})
;; => {:Buckets [{:Name <name> :CreationDate <date> ,,,}]}

;; http-request and http-response are in the metadata
(meta *1)
;; => {:http-request {:request-method :get,
;;                    :scheme :https,
;;                    :server-port 443,
;;                    :uri "/",
;;                    :headers {,,,},
;;                    :server-name "s3.amazonaws.com",
;;                    :body nil},
;;     :http-response {:status 200,
;;                     :headers {,,,},
;;                     :body <input-stream>}
clj꞉user꞉> 

;; create a bucket in the same region as the client
(aws/invoke s3 {:op :CreateBucket :request {:Bucket "my-unique-bucket-name"}})

;; create a bucket in a region other than us-east-1
(aws/invoke s3 {:op :CreateBucket :request {:Bucket "my-unique-bucket-name-in-us-west-1"
                                            :CreateBucketConfiguration
                                            {:LocationConstraint "us-west-1"}}})

;; NOTE: be sure to create a client with region "us-west-1" when accessing that
;; bucket.

(aws/invoke s3 {:op :ListBuckets})

See the examples directory for more examples.

Responses, successes, redirects, and failures

Barring client side exceptions, every operation on every AWS service returns a map. If the operation is successful, the map is in the shape described by (-> client aws/ops op :response). AWS documents all HTTP status codes >= 300 as errors (see https://docs.aws.amazon.com/AmazonS3/latest/API/ErrorResponses.html), so when AWS returns an HTTP status code >= 300, aws-api returns an anomaly map, identified by a :cognitect.anomalies/category key, with the HTTP status bound to a :cognitect.aws.http/status key. When AWS provides an error response in the HTTP response body, aws-api coerces it to clojure data, and merges that into the anomaly map. Additionally, when AWS provides an error code, aws-api will bind it to a :cognitect.aws.error/code key. Example:

{:Error                                                        ;; provided by AWS
 {:Message "The specified key does not exist."                 ;; provided by AWS
  :Code "NoSuchKey"}                                           ;; provided by AWS
 :cognitect.anomalies/category :cognitect.anomalies/not-found
 :cognitect.aws.http/status 404
 :cognitect.aws.error/code "NoSuchKey"}                        ;; derived from :Code, above

If you need more information when you receive an anomaly map, you can check (-> response meta :http-response) for the raw http response, including the :status and :headers.

S3 GetObject and Conditional Requests

S3 GetObject supports Conditional Requests with :IfMatch, :IfNoneMatch, :IfModifiedSince, and :IfUnmodifiedSince, which may result in 304s (for :IfNoneMatch and :IfModifiedSince) or 412s (for :IfMatch, and :IfUnmodifiedSince). AWS documents all of these as errors, and AWS SDKs throw exceptions for 412s and 304s. aws-api returns anomalies instead of throwing exceptions, so aws-api will return anomalies for both 412s and 304s.

Error responses with status 200

Per https://aws.amazon.com/premiumsupport/knowledge-center/s3-resolve-200-internalerror/, AWS may return a 200 with an error response in the body, in which case you should look for an error code in the body.

Credentials

The aws-api client implicitly looks up credentials the same way the java SDK does.

To provide credentials explicitly, you pass an implementation of cognitect.aws.credentials/CredentialsProvider to the client constructor fn, .e.g

(require '[cognitect.aws.client.api :as aws])
(def kms (aws/client {:api :kms :credentials-provider my-custom-provider}))

If you're supplying a known access-key/secret pair, you can use the basic-credentials-provider helper fn:

(require '[cognitect.aws.client.api :as aws]
         '[cognitect.aws.credentials :as credentials])

(def kms (aws/client {:api                  :kms
                      :credentials-provider (credentials/basic-credentials-provider
                                             {:access-key-id     "ABC"
                                              :secret-access-key "XYZ"})}))

See the assume role example for a more involved example using AWS STS.

Region lookup

The aws-api client looks up the region the same way the java SDK does, with an additional check for a System property named "aws.region" after it checks for the AWS_REGION environment variable and before it checks your aws configuration.

Endpoint Override

Most of the time you can create a client and it figures out the correct endpoint for you. The endpoints of most AWS API operations adhere to the pattern documented in AWS Regions and Endpoints. But there are exceptions.

  • Some AWS APIs have operations which require custom endpoints (e.g. Kinesis Video GetMedia).
  • You may want to use a proxy server or connect to a local dynamodb.
  • Perhaps you've found a bug that you could work around if you could supply the correct endpoint.

All of this can be accomplished by supplying an :endpoint-override map to the client constructor:

(def ddb (aws/client {:api :dynamodb
                      :endpoint-override {:protocol :http
                                          :hostname "localhost"
                                          :port     8000}}))

Testing

aws-api provides a test-double client you can use to simulate aws/invoke in your tests.

See https://github.com/cognitect-labs/aws-api/blob/main/doc/testing.md.

PostToConnection

The :PostToConnection operation on the apigatewaymanagementapi client requires that you specify the API endpoint as follows:

(def client (aws/client {:api :apigatewaymanagementapi
                         :endpoint-override {:hostname "{hostname}"
                                             :path "/{stage}/@connections/"}}))

Replace {hostname} and {stage} with the hostname and the stage of the connection to which you're posting (see https://docs.aws.amazon.com/apigateway/latest/developerguide/apigateway-how-to-call-websocket-api-connections.html).

The client will append the :ConnectionId in the :request map to the :path in the :endpoint-override map.

http-client

NOTE: the behavior of com.cognitect.aws.api/client and com.cognitect.aws.api/stop changed as of release 0.8.430. See Upgrade Notes for more information.

The aws-api client uses an http-client to send requests to AWS, including any operations you invoke and fetching the region and credentials when you're running in EC2 or ECS. By default, each aws-api client uses a single, shared http-client, whose resources are managed by aws-api.

Troubleshooting

Retriable errors

When the aws-api client encounters an error, it uses two funtions to determine whether to retry the request:

(retriable? [anomaly]
  ;; should return a truthy value when the anomaly* indicates that
  ;; the request is retriable.
  )

;; Then, if retriable? returns a truthy value:

(backoff [n-tries-so-far]
  ;; should return the number of milliseconds to wait before trying
  ;; again, or nil, which indicates that we have reached the max number
  ;; of retries and should not try again.
  )

*see Cognitect anomalies

The defaults for these are:

cognitect.aws.retry/default-retriable?
cognitect.aws.retry/default-backoff

You can override these defaults by passing functions to cognitect.aws.client.api/client bound to the keys :retriable? and :backoff, e.g.

(cognitect.aws.client.api/client
  {:api        :iam
   :retriable? custom-retriable-fn
   :backoff    custom-backoff-fn})

default retriable?

The default retriable predicate, cognitect.aws.retry/default-retriable?, returns a truthy value when the value of :cognitect.anomalies/category is any of:

  • :cognitect.anomalies/busy
  • :cognitect.anomalies/interrupted
  • :cognitect.anomalies/unavailable

Because we do not control the sources of these errors, we cannot guarantee that every retriable error will be recognized. If you encounter an error that you think should be retriable, you can supply a custom predicate bound to the :retriable? key when you create a client.

(cognitect.aws.client.api/client
  {:api        :iam
   :retriable? (fn [{:keys [cognitect.anomalies/category] :as error-info] ,,)})

Only cognitect.anomalies/category is controlled by aws-api, and you should inspect the actual error to understand what other information is available to you to decide whether or not a request is retriable.

default backoff

The default backoff, cognitect.aws.retry/default-backoff, is a capped, exponential backoff, which returns nil after max-retries have already been attempted.

If you wish to override this backoff strategy, you can supply a custom function bound to the :backoff key when you create a client.

(cognitect.aws.client.api/client
  {:api     :iam
   :backoff (fn [n-tries-so-far] ,,)})

Don't forget to account for termination by returning nil after some number of retries.

You an also use cognitect.aws.retry/capped-exponential-backoff to generate a function with different values for base, max-backoff, and max-retries, and then pass that to client.

nodename nor servname provided, or not known

This indicates that the configured endpoint is incorrect for the service/op you are trying to perform.

Remedy: check AWS Regions and Endpoints for the proper endpoint and use the :endpoint-override key when creating a client, e.g.

(def s3-control {:api :s3control})
(aws/client {:api :s3control
             :endpoint-override {:hostname (str my-account-id ".s3-control.us-east-1.amazonaws.com")}})

UnknownOperationException

AWS will return an UnknownOperationException response when a client is configured with (or defaults to) an incorrect endpoint.

Remedy: check AWS Regions and Endpoints for the proper endpoint and use the :endpoint-override key when creating a client.

Note that some AWS APIs have custom endpoint requirements. For example, Kinesis Video Get Media operation requires a custom endpoint, e.g.

(def kvs (aws/client {:api :kinesisvideo ... }))

(def kvs-endpoint (:DataEndpoint (aws/invoke kvs {:op :GetDataEndpoint ... })))

(aws/client {:api :kinesis-video-media
             :region "us-east-1"
             :endpoint-override {:hostname (str/replace kvs-endpoint #"https:\/\/" "")}})

No known endpoint.

This indicates that the data in the com.cognitect.aws/endpoints lib (which is derived from endpoints.json) does not support the :api/:region combination you are trying to access.

Remedy: check AWS Regions and Endpoints, and supply the correct endpoint as described in nodename nor servname provided, or not known, above.

Ops limit reached

The underlying http-client has a :pending-ops-limit configuration which, when reached, results in an exception with the message "Ops limit reached". As of this writing, aws-api does not provide access to the http-client's configuration. Programs that encounter "Ops limit reached" can avoid it by creating separate http-clients for each aws-client. You may wish to explicitly stop (com.cognitect.aws.api/stop) these aws-clients when the are not longer in use to conserve resources.

S3: "Invalid 'Location' header: null"

This indicates that you are trying to access a resource that resides in a different region from that of the client.

As of v0.8.670, instead of this error, you'll see an AWS-provided payload decorated with information about how to recover.

As of v0.8.662, the anomaly also includes status 301 and the "x-amz-bucket-region" header, so you can now detect the 301 and create a new client in the region bound to the "x-amz-bucket-region" header.

If you're using a version older than 0.8.662, you'll have to figure out the region out of band (AWS console, etc).

Contributing

aws-api is open source, developed internally at Nubank. Issues can be filed using GitHub issues for this project. Because aws-api is incorporated into products, we prefer to do development internally and are not accepting pull requests or patches.

Contributors

aws-api was extracted from an internal project at Cognitect, and some contributors are missing from the commit log. Here are all the folks from Cognitect and Nubank who either committed code directly, or contributed significantly to research and design:

Timothy Baldridge
Scott Bale
David Chelimsky
Maria Clara Crespo
Benoît Fleury
Fogus
Kyle Gann
Stuart Halloway
Rich Hickey
George Kierstein
Carin Meier
Joe Lane
Alex Miller
Michael Nygard
Ghadi Shayban
Joseph Smith
Thayanne Sousa
Marshall Thompson

Copyright and License

Copyright © 2015 Cognitect

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.