Lambda docs (#264)

* Add aws.md and s3 example

Signed-off-by: Seif Lotfy <seif.lotfy@gmail.com>

* minor fix

examples/s3/Dockerfile

@@ -0,0 +1,5 @@
+FROM iron/lambda-nodejs
+
+ADD example.js ./example.js
+
+CMD ["example.run"]

examples/s3/Makefile

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+IMAGE=iron/lambda-node-aws-example
+
+create: Dockerfile
+	docker build -t $(IMAGE) .
+
+test:
+	docker run --rm -it -e PAYLOAD_FILE=/mnt/example-payload.json -e AWS_ACCESS_KEY_ID=change-here -e AWS_SECRET_ACCESS_KEY=change-here -v `pwd`:/mnt $(IMAGE)

examples/s3/README.md

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+Example on how to use AWS S3 in a lambda function.
+

examples/s3/example-payload.json

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+{
+    "bucket": "iron-lambda-demo-images",
+    "srcKey": "waterfall.jpg", 
+    "dstKey": "waterfall-1024.jpg"
+}

examples/s3/example.js

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+var im = require('imagemagick');
+var fs = require('fs');
+var AWS = require('aws-sdk');
+
+// cb(err, resized) is called with true if resized.
+function resizeIfRequired(err, features, fileSrc, fileDst, cb) {
+  if (err) {
+    cb(err, false);
+    return;
+  }
+
+  var targetWidth = 1024;
+  if (features.width > targetWidth)
+  {
+    im.resize({
+      srcPath : fileSrc,
+      dstPath : fileDst,
+      width : targetWidth,
+      format: 'jpg'
+    }, function(err) {
+      if (err) {
+        cb(err, false);
+      } else {
+        cb(null, true);
+      }
+    });
+  } else {
+    cb(null, false);
+  }
+}
+
+exports.run = function(event, context) {
+  var bucketName = event['bucket']
+  var srcImageKey = event['srcKey']
+  var dstImageKey = event['dstKey']
+
+  var s3 = new AWS.S3();
+
+  s3.getObject({
+      Bucket: bucketName,
+      Key: srcImageKey
+    }, function (err, data) {
+
+    if (err) throw err;
+
+    var fileSrc = '/tmp/image-src.dat';
+    var fileDst = '/tmp/image-dst.dat'
+    fs.writeFileSync(fileSrc, data.Body)
+
+    im.identify(fileSrc, function(err, features) {
+      resizeIfRequired(err, features, fileSrc, fileDst, function(err, resized) {
+        if (err) throw err;
+        if (resized) {
+          s3.putObject({
+            Bucket:bucketName,
+            Key: dstImageKey,
+            Body: fs.createReadStream(fileDst),
+            ContentType: 'image/jpeg',
+            ACL: 'public-read',
+          }, function (err, data) {
+            if (err) throw err;
+            context.succeed("Image updated");
+          });
+        } else {
+          context.succeed("Image not updated");
+        }
+      });
+    });
+  });
+}