This adds a method to the Driver: PreCreateCheck. This can be used

where you want to run some prerequisite checks before attempting to
create
the machine.  In the case of EC2, this is a check for an existing
keypair.  This can be used in the other drivers in the future as well.

Signed-off-by: Evan Hazlett <ejhazlett@gmail.com>

drivers/amazonec2/amazonec2.go

@@ -182,7 +182,28 @@ func (d *Driver) DriverName() string {
 	return driverName
 }
 
+func (d *Driver) checkPrereqs() error {
+	// check for existing keypair
+	key, err := d.getClient().GetKeyPair(d.MachineName)
+	if err != nil {
+		return err
+	}
+
+	if key != nil {
+		return fmt.Errorf("There is already a keypair with the name %s.  Please either remove that keypair or use a different machine name.", d.MachineName)
+	}
+	return nil
+}
+
+func (d *Driver) PreCreateCheck() error {
+	return d.checkPrereqs()
+}
+
 func (d *Driver) Create() error {
+	if err := d.checkPrereqs(); err != nil {
+		return err
+	}
+
 	log.Infof("Launching instance...")
 
 	if err := d.createKeyPair(); err != nil {

drivers/amazonec2/amz/describe_keypairs.go

@@ -0,0 +1,6 @@
+package amz
+
+type DescribeKeyPairsResponse struct {
+	RequestId string    `xml:"requestId"`
+	KeySet    []KeyPair `xml:"keySet>item"`
+}

drivers/amazonec2/amz/ec2.go

@@ -438,6 +438,42 @@ func (e *EC2) GetSubnets() ([]Subnet, error) {
 	return subnets, nil
 }
 
+func (e *EC2) GetKeyPairs() ([]KeyPair, error) {
+	keyPairs := []KeyPair{}
+	resp, err := e.performStandardAction("DescribeKeyPairs")
+	if err != nil {
+		return keyPairs, err
+	}
+	defer resp.Body.Close()
+	contents, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return keyPairs, fmt.Errorf("Error reading AWS response body: %s", err)
+	}
+
+	unmarshalledResponse := DescribeKeyPairsResponse{}
+	if err = xml.Unmarshal(contents, &unmarshalledResponse); err != nil {
+		return keyPairs, fmt.Errorf("Error unmarshalling AWS response XML: %s", err)
+	}
+
+	keyPairs = unmarshalledResponse.KeySet
+
+	return keyPairs, nil
+}
+
+func (e *EC2) GetKeyPair(name string) (*KeyPair, error) {
+	keyPairs, err := e.GetKeyPairs()
+	if err != nil {
+		return nil, err
+	}
+
+	for _, key := range keyPairs {
+		if key.KeyName == name {
+			return &key, nil
+		}
+	}
+	return nil, nil
+}
+
 func (e *EC2) GetInstanceState(instanceId string) (state.State, error) {
 	resp, err := e.performInstanceAction(instanceId, "DescribeInstances", nil)
 	if err != nil {

drivers/amazonec2/amz/keypair.go

@@ -11,3 +11,8 @@ type ImportKeyPairResponse struct {
 	KeyFingerprint string `xml:"keyFingerprint"`
 	KeyMaterial    []byte `xml:"keyMaterial"`
 }
+
+type KeyPair struct {
+	KeyFingerprint string `xml:"keyFingerprint"`
+	KeyName        string `xml:"keyName"`
+}