You are viewing a plain text version of this content. The canonical link for it is here.
Posted to dev@druid.apache.org by Dongjin Lee <do...@apache.org> on 2018/07/25 04:47:20 UTC
Problem on druid-s3-extensions
Hello. I encountered a problem building druid. *In short,
`TestAWSCredentialsProvider` fails like the following*:
```
mvn -pl extensions-core/s3-extensions test
...
testWithFileSessionCredentials(io.druid.storage.s3.TestAWSCredentialsProvider)
Time elapsed: 6.615 sec <<< ERROR!
com.amazonaws.SdkClientException: Unable to find a region via the region
provider chain. Must provide an explicit region in the builder or setup
environment to supply a region.
at
io.druid.storage.s3.TestAWSCredentialsProvider.testWithFileSessionCredentials(TestAWSCredentialsProvider.java:98)
testWithFixedAWSKeys(io.druid.storage.s3.TestAWSCredentialsProvider) Time
elapsed: 4.345 sec <<< ERROR!
com.amazonaws.SdkClientException: Unable to find a region via the region
provider chain. Must provide an explicit region in the builder or setup
environment to supply a region.
at
io.druid.storage.s3.TestAWSCredentialsProvider.testWithFixedAWSKeys(TestAWSCredentialsProvider.java:67)
```
After digging the code, I found following:
1. `S3StorageDruidModule` does not provide a way to explictily set
`Region`, but detects the region automatically with its default
credential/region provider chain. `S3StorageDruidModule#getAmazonS3Client
-> AmazonS3Client#builder -> AmazonS3ClientBuilder#standard;`
2. The default region provider chain[^1][^2] tries to determine region in
following orders:[^1][^2]
a. Environment Variable[^5]
b. JVM property[^6]
c. AWS Configuration[^7]
d. EC2 instance metadata service[^8]
If all of the above fails, it throws an Exception.
*In short, there is a possibility that `S3StorageDruidModule` can't
determine the Region. It would be better to provide a way to set Region
explicitly.*
How do you think?
Best,
Dongjin
[^1]:
https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/DefaultAwsRegionProviderChain.java
[^2]:
https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsRegionProviderChain.java
[^3]:
https://docs.aws.amazon.com/sdk-for-java/v2/developer-guide/java-dg-region-selection.html
[^4]: The example client in documentation is `AmazonEC2ClientBuilder` but
it also applies to the other clients like `AmazonS3ClientBuilder`.
[^5]:
https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsEnvVarOverrideRegionProvider.java
[^6]:
https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsSystemPropertyRegionProvider.java
[^7]:
https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsProfileRegionProvider.java
[^8]:
https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/InstanceMetadataRegionProvider.java
--
*Dongjin Lee*
*A hitchhiker in the mathematical world.*
*github: <http://goog_969573159/>github.com/dongjinleekr
<http://github.com/dongjinleekr>linkedin: kr.linkedin.com/in/dongjinleekr
<http://kr.linkedin.com/in/dongjinleekr>slideshare:
www.slideshare.net/dongjinleekr
<http://www.slideshare.net/dongjinleekr>*
Re: Problem on druid-s3-extensions
Posted by Dongjin Lee <do...@apache.org>.
I greatly appreciate your guidance. Now all the tests pass well!
Thanks,
Dongjin
On Thu, Jul 26, 2018 at 3:27 AM Jihoon Son <gh...@gmail.com> wrote:
> Hi Dongjin,
>
> as Charles said, you should set the region for aws sdk. Here is a snippet
> of our Travis configuration.
>
> > # other modules test
> > - sudo: false
> > env:
> > - NAME="other modules test"
> > - AWS_REGION=us-east-1 # set a aws region for unit tests
> > install: echo "MAVEN_OPTS='-Xmx3000m'" > ~/.mavenrc && mvn install
> -q -ff -DskipTests -B
> > before_script:
> > - unset _JAVA_OPTIONS
> > script: echo "MAVEN_OPTS='-Xmx512m'" > ~/.mavenrc && mvn test -B
> -Pparallel-test -Dmaven.fork.count=2 -pl '!processing,!server'
>
> Jihoon
>
> On Wed, Jul 25, 2018 at 8:29 AM Charles Allen
> <ch...@snap.com.invalid> wrote:
>
> > IMHO the best way to do it would be to setup the test so that it sets the
> > region just for the test, and let production systems use whichever region
> > provider fits the way they typically do region configs. That way people
> > running the tests don't have to worry about anything regarding how to
> setup
> > a region, and people deploying cloud services don't have surprise
> behavior
> > for Druid compared to other usages of the java sdk.
> >
> > On Tue, Jul 24, 2018 at 9:48 PM Dongjin Lee <do...@apache.org> wrote:
> >
> > > Hello. I encountered a problem building druid. *In short,
> > > `TestAWSCredentialsProvider` fails like the following*:
> > >
> > > ```
> > > mvn -pl extensions-core/s3-extensions test
> > >
> > > ...
> > >
> > >
> > >
> >
> testWithFileSessionCredentials(io.druid.storage.s3.TestAWSCredentialsProvider)
> > > Time elapsed: 6.615 sec <<< ERROR!
> > > com.amazonaws.SdkClientException: Unable to find a region via the
> region
> > > provider chain. Must provide an explicit region in the builder or setup
> > > environment to supply a region.
> > > at
> > >
> > >
> >
> io.druid.storage.s3.TestAWSCredentialsProvider.testWithFileSessionCredentials(TestAWSCredentialsProvider.java:98)
> > >
> > > testWithFixedAWSKeys(io.druid.storage.s3.TestAWSCredentialsProvider)
> > Time
> > > elapsed: 4.345 sec <<< ERROR!
> > > com.amazonaws.SdkClientException: Unable to find a region via the
> region
> > > provider chain. Must provide an explicit region in the builder or setup
> > > environment to supply a region.
> > > at
> > >
> > >
> >
> io.druid.storage.s3.TestAWSCredentialsProvider.testWithFixedAWSKeys(TestAWSCredentialsProvider.java:67)
> > > ```
> > >
> > > After digging the code, I found following:
> > >
> > > 1. `S3StorageDruidModule` does not provide a way to explictily set
> > > `Region`, but detects the region automatically with its default
> > > credential/region provider chain.
> `S3StorageDruidModule#getAmazonS3Client
> > > -> AmazonS3Client#builder -> AmazonS3ClientBuilder#standard;`
> > > 2. The default region provider chain[^1][^2] tries to determine region
> in
> > > following orders:[^1][^2]
> > > a. Environment Variable[^5]
> > > b. JVM property[^6]
> > > c. AWS Configuration[^7]
> > > d. EC2 instance metadata service[^8]
> > >
> > > If all of the above fails, it throws an Exception.
> > >
> > > *In short, there is a possibility that `S3StorageDruidModule` can't
> > > determine the Region. It would be better to provide a way to set Region
> > > explicitly.*
> > >
> > > How do you think?
> > >
> > > Best,
> > > Dongjin
> > >
> > > [^1]:
> > >
> > >
> >
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/DefaultAwsRegionProviderChain.java
> > > [^2]:
> > >
> > >
> >
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsRegionProviderChain.java
> > > [^3]:
> > >
> > >
> >
> https://urldefense.proofpoint.com/v2/url?u=https-3A__docs.aws.amazon.com_sdk-2Dfor-2Djava_v2_developer-2Dguide_java-2Ddg-2Dregion-2Dselection.html&d=DwIBaQ&c=ncDTmphkJTvjIDPh0hpF_w&r=HrLGT1qWNhseJBMYABL0GFSZESht5gBoLejor3SqMSo&m=KVjSJAnGDSKgdNTP-vCFDAUpnrBBYAiix7JzjxvHuwI&s=Ro8j9Jj9lCbFbc0aYDNjwtZuD2a_9fPaYw1lOp7ZQeQ&e=
> > > [^4]: The example client in documentation is `AmazonEC2ClientBuilder`
> but
> > > it also applies to the other clients like `AmazonS3ClientBuilder`.
> > > [^5]:
> > >
> > >
> >
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsEnvVarOverrideRegionProvider.java
> > > [^6]:
> > >
> > >
> >
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsSystemPropertyRegionProvider.java
> > > [^7]:
> > >
> > >
> >
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsProfileRegionProvider.java
> > > [^8]:
> > >
> > >
> >
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/InstanceMetadataRegionProvider.java
> > >
> > > --
> > > *Dongjin Lee*
> > >
> > > *A hitchhiker in the mathematical world.*
> > >
> > > *github: <
> > >
> >
> https://urldefense.proofpoint.com/v2/url?u=http-3A__goog-5F969573159_&d=DwIBaQ&c=ncDTmphkJTvjIDPh0hpF_w&r=HrLGT1qWNhseJBMYABL0GFSZESht5gBoLejor3SqMSo&m=KVjSJAnGDSKgdNTP-vCFDAUpnrBBYAiix7JzjxvHuwI&s=VLpmOvpUoEqDfaI8jAV3WKsttHGasxSzCwmAE-we-CU&e=
> > > >github.com/dongjinleekr
> > > <http://github.com/dongjinleekr>linkedin:
> > kr.linkedin.com/in/dongjinleekr
> > > <
> > >
> >
> https://urldefense.proofpoint.com/v2/url?u=http-3A__kr.linkedin.com_in_dongjinleekr&d=DwIBaQ&c=ncDTmphkJTvjIDPh0hpF_w&r=HrLGT1qWNhseJBMYABL0GFSZESht5gBoLejor3SqMSo&m=KVjSJAnGDSKgdNTP-vCFDAUpnrBBYAiix7JzjxvHuwI&s=LnjNxyq941KadHM075fCkotIkN-U4USFaqm2JsKi08Q&e=
> > > >slideshare:
> > > www.slideshare.net/dongjinleekr
> > > <
> > >
> >
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.slideshare.net_dongjinleekr&d=DwIBaQ&c=ncDTmphkJTvjIDPh0hpF_w&r=HrLGT1qWNhseJBMYABL0GFSZESht5gBoLejor3SqMSo&m=KVjSJAnGDSKgdNTP-vCFDAUpnrBBYAiix7JzjxvHuwI&s=hoP7U3GI-oMiDEdyIocsIkBAoupeT_QQ52PBHlEeoUQ&e=
> > > >*
> > >
> >
>
> --
> *Dongjin Lee*
>
> *A hitchhiker in the mathematical world.*
>
> *github: <http://goog_969573159/>github.com/dongjinleekr
> <http://github.com/dongjinleekr>linkedin: kr.linkedin.com/in/dongjinleekr
> <http://kr.linkedin.com/in/dongjinleekr>slideshare: www.slideshare.net/dongjinleekr
> <http://www.slideshare.net/dongjinleekr>*
>
Re: Problem on druid-s3-extensions
Posted by Jihoon Son <gh...@gmail.com>.
Hi Dongjin,
as Charles said, you should set the region for aws sdk. Here is a snippet
of our Travis configuration.
> # other modules test
> - sudo: false
> env:
> - NAME="other modules test"
> - AWS_REGION=us-east-1 # set a aws region for unit tests
> install: echo "MAVEN_OPTS='-Xmx3000m'" > ~/.mavenrc && mvn install
-q -ff -DskipTests -B
> before_script:
> - unset _JAVA_OPTIONS
> script: echo "MAVEN_OPTS='-Xmx512m'" > ~/.mavenrc && mvn test -B
-Pparallel-test -Dmaven.fork.count=2 -pl '!processing,!server'
Jihoon
On Wed, Jul 25, 2018 at 8:29 AM Charles Allen
<ch...@snap.com.invalid> wrote:
> IMHO the best way to do it would be to setup the test so that it sets the
> region just for the test, and let production systems use whichever region
> provider fits the way they typically do region configs. That way people
> running the tests don't have to worry about anything regarding how to setup
> a region, and people deploying cloud services don't have surprise behavior
> for Druid compared to other usages of the java sdk.
>
> On Tue, Jul 24, 2018 at 9:48 PM Dongjin Lee <do...@apache.org> wrote:
>
> > Hello. I encountered a problem building druid. *In short,
> > `TestAWSCredentialsProvider` fails like the following*:
> >
> > ```
> > mvn -pl extensions-core/s3-extensions test
> >
> > ...
> >
> >
> >
> testWithFileSessionCredentials(io.druid.storage.s3.TestAWSCredentialsProvider)
> > Time elapsed: 6.615 sec <<< ERROR!
> > com.amazonaws.SdkClientException: Unable to find a region via the region
> > provider chain. Must provide an explicit region in the builder or setup
> > environment to supply a region.
> > at
> >
> >
> io.druid.storage.s3.TestAWSCredentialsProvider.testWithFileSessionCredentials(TestAWSCredentialsProvider.java:98)
> >
> > testWithFixedAWSKeys(io.druid.storage.s3.TestAWSCredentialsProvider)
> Time
> > elapsed: 4.345 sec <<< ERROR!
> > com.amazonaws.SdkClientException: Unable to find a region via the region
> > provider chain. Must provide an explicit region in the builder or setup
> > environment to supply a region.
> > at
> >
> >
> io.druid.storage.s3.TestAWSCredentialsProvider.testWithFixedAWSKeys(TestAWSCredentialsProvider.java:67)
> > ```
> >
> > After digging the code, I found following:
> >
> > 1. `S3StorageDruidModule` does not provide a way to explictily set
> > `Region`, but detects the region automatically with its default
> > credential/region provider chain. `S3StorageDruidModule#getAmazonS3Client
> > -> AmazonS3Client#builder -> AmazonS3ClientBuilder#standard;`
> > 2. The default region provider chain[^1][^2] tries to determine region in
> > following orders:[^1][^2]
> > a. Environment Variable[^5]
> > b. JVM property[^6]
> > c. AWS Configuration[^7]
> > d. EC2 instance metadata service[^8]
> >
> > If all of the above fails, it throws an Exception.
> >
> > *In short, there is a possibility that `S3StorageDruidModule` can't
> > determine the Region. It would be better to provide a way to set Region
> > explicitly.*
> >
> > How do you think?
> >
> > Best,
> > Dongjin
> >
> > [^1]:
> >
> >
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/DefaultAwsRegionProviderChain.java
> > [^2]:
> >
> >
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsRegionProviderChain.java
> > [^3]:
> >
> >
> https://urldefense.proofpoint.com/v2/url?u=https-3A__docs.aws.amazon.com_sdk-2Dfor-2Djava_v2_developer-2Dguide_java-2Ddg-2Dregion-2Dselection.html&d=DwIBaQ&c=ncDTmphkJTvjIDPh0hpF_w&r=HrLGT1qWNhseJBMYABL0GFSZESht5gBoLejor3SqMSo&m=KVjSJAnGDSKgdNTP-vCFDAUpnrBBYAiix7JzjxvHuwI&s=Ro8j9Jj9lCbFbc0aYDNjwtZuD2a_9fPaYw1lOp7ZQeQ&e=
> > [^4]: The example client in documentation is `AmazonEC2ClientBuilder` but
> > it also applies to the other clients like `AmazonS3ClientBuilder`.
> > [^5]:
> >
> >
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsEnvVarOverrideRegionProvider.java
> > [^6]:
> >
> >
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsSystemPropertyRegionProvider.java
> > [^7]:
> >
> >
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsProfileRegionProvider.java
> > [^8]:
> >
> >
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/InstanceMetadataRegionProvider.java
> >
> > --
> > *Dongjin Lee*
> >
> > *A hitchhiker in the mathematical world.*
> >
> > *github: <
> >
> https://urldefense.proofpoint.com/v2/url?u=http-3A__goog-5F969573159_&d=DwIBaQ&c=ncDTmphkJTvjIDPh0hpF_w&r=HrLGT1qWNhseJBMYABL0GFSZESht5gBoLejor3SqMSo&m=KVjSJAnGDSKgdNTP-vCFDAUpnrBBYAiix7JzjxvHuwI&s=VLpmOvpUoEqDfaI8jAV3WKsttHGasxSzCwmAE-we-CU&e=
> > >github.com/dongjinleekr
> > <http://github.com/dongjinleekr>linkedin:
> kr.linkedin.com/in/dongjinleekr
> > <
> >
> https://urldefense.proofpoint.com/v2/url?u=http-3A__kr.linkedin.com_in_dongjinleekr&d=DwIBaQ&c=ncDTmphkJTvjIDPh0hpF_w&r=HrLGT1qWNhseJBMYABL0GFSZESht5gBoLejor3SqMSo&m=KVjSJAnGDSKgdNTP-vCFDAUpnrBBYAiix7JzjxvHuwI&s=LnjNxyq941KadHM075fCkotIkN-U4USFaqm2JsKi08Q&e=
> > >slideshare:
> > www.slideshare.net/dongjinleekr
> > <
> >
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.slideshare.net_dongjinleekr&d=DwIBaQ&c=ncDTmphkJTvjIDPh0hpF_w&r=HrLGT1qWNhseJBMYABL0GFSZESht5gBoLejor3SqMSo&m=KVjSJAnGDSKgdNTP-vCFDAUpnrBBYAiix7JzjxvHuwI&s=hoP7U3GI-oMiDEdyIocsIkBAoupeT_QQ52PBHlEeoUQ&e=
> > >*
> >
>
Re: Problem on druid-s3-extensions
Posted by Charles Allen <ch...@snap.com.INVALID>.
IMHO the best way to do it would be to setup the test so that it sets the
region just for the test, and let production systems use whichever region
provider fits the way they typically do region configs. That way people
running the tests don't have to worry about anything regarding how to setup
a region, and people deploying cloud services don't have surprise behavior
for Druid compared to other usages of the java sdk.
On Tue, Jul 24, 2018 at 9:48 PM Dongjin Lee <do...@apache.org> wrote:
> Hello. I encountered a problem building druid. *In short,
> `TestAWSCredentialsProvider` fails like the following*:
>
> ```
> mvn -pl extensions-core/s3-extensions test
>
> ...
>
>
> testWithFileSessionCredentials(io.druid.storage.s3.TestAWSCredentialsProvider)
> Time elapsed: 6.615 sec <<< ERROR!
> com.amazonaws.SdkClientException: Unable to find a region via the region
> provider chain. Must provide an explicit region in the builder or setup
> environment to supply a region.
> at
>
> io.druid.storage.s3.TestAWSCredentialsProvider.testWithFileSessionCredentials(TestAWSCredentialsProvider.java:98)
>
> testWithFixedAWSKeys(io.druid.storage.s3.TestAWSCredentialsProvider) Time
> elapsed: 4.345 sec <<< ERROR!
> com.amazonaws.SdkClientException: Unable to find a region via the region
> provider chain. Must provide an explicit region in the builder or setup
> environment to supply a region.
> at
>
> io.druid.storage.s3.TestAWSCredentialsProvider.testWithFixedAWSKeys(TestAWSCredentialsProvider.java:67)
> ```
>
> After digging the code, I found following:
>
> 1. `S3StorageDruidModule` does not provide a way to explictily set
> `Region`, but detects the region automatically with its default
> credential/region provider chain. `S3StorageDruidModule#getAmazonS3Client
> -> AmazonS3Client#builder -> AmazonS3ClientBuilder#standard;`
> 2. The default region provider chain[^1][^2] tries to determine region in
> following orders:[^1][^2]
> a. Environment Variable[^5]
> b. JVM property[^6]
> c. AWS Configuration[^7]
> d. EC2 instance metadata service[^8]
>
> If all of the above fails, it throws an Exception.
>
> *In short, there is a possibility that `S3StorageDruidModule` can't
> determine the Region. It would be better to provide a way to set Region
> explicitly.*
>
> How do you think?
>
> Best,
> Dongjin
>
> [^1]:
>
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/DefaultAwsRegionProviderChain.java
> [^2]:
>
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsRegionProviderChain.java
> [^3]:
>
> https://urldefense.proofpoint.com/v2/url?u=https-3A__docs.aws.amazon.com_sdk-2Dfor-2Djava_v2_developer-2Dguide_java-2Ddg-2Dregion-2Dselection.html&d=DwIBaQ&c=ncDTmphkJTvjIDPh0hpF_w&r=HrLGT1qWNhseJBMYABL0GFSZESht5gBoLejor3SqMSo&m=KVjSJAnGDSKgdNTP-vCFDAUpnrBBYAiix7JzjxvHuwI&s=Ro8j9Jj9lCbFbc0aYDNjwtZuD2a_9fPaYw1lOp7ZQeQ&e=
> [^4]: The example client in documentation is `AmazonEC2ClientBuilder` but
> it also applies to the other clients like `AmazonS3ClientBuilder`.
> [^5]:
>
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsEnvVarOverrideRegionProvider.java
> [^6]:
>
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsSystemPropertyRegionProvider.java
> [^7]:
>
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/AwsProfileRegionProvider.java
> [^8]:
>
> https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-core/src/main/java/com/amazonaws/regions/InstanceMetadataRegionProvider.java
>
> --
> *Dongjin Lee*
>
> *A hitchhiker in the mathematical world.*
>
> *github: <
> https://urldefense.proofpoint.com/v2/url?u=http-3A__goog-5F969573159_&d=DwIBaQ&c=ncDTmphkJTvjIDPh0hpF_w&r=HrLGT1qWNhseJBMYABL0GFSZESht5gBoLejor3SqMSo&m=KVjSJAnGDSKgdNTP-vCFDAUpnrBBYAiix7JzjxvHuwI&s=VLpmOvpUoEqDfaI8jAV3WKsttHGasxSzCwmAE-we-CU&e=
> >github.com/dongjinleekr
> <http://github.com/dongjinleekr>linkedin: kr.linkedin.com/in/dongjinleekr
> <
> https://urldefense.proofpoint.com/v2/url?u=http-3A__kr.linkedin.com_in_dongjinleekr&d=DwIBaQ&c=ncDTmphkJTvjIDPh0hpF_w&r=HrLGT1qWNhseJBMYABL0GFSZESht5gBoLejor3SqMSo&m=KVjSJAnGDSKgdNTP-vCFDAUpnrBBYAiix7JzjxvHuwI&s=LnjNxyq941KadHM075fCkotIkN-U4USFaqm2JsKi08Q&e=
> >slideshare:
> www.slideshare.net/dongjinleekr
> <
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.slideshare.net_dongjinleekr&d=DwIBaQ&c=ncDTmphkJTvjIDPh0hpF_w&r=HrLGT1qWNhseJBMYABL0GFSZESht5gBoLejor3SqMSo&m=KVjSJAnGDSKgdNTP-vCFDAUpnrBBYAiix7JzjxvHuwI&s=hoP7U3GI-oMiDEdyIocsIkBAoupeT_QQ52PBHlEeoUQ&e=
> >*
>