How do I write a buildspec.yml file?
Few ideas to help you


When you define a "CodeBuild" project, you can specify which base image it will use to execute your commands. The one you are using is not Ubuntu yet you are trying apt-get. Try a different base image.
Provide us with a better log stream.


Exporting Logs from CloudWatch

I found that the easiest way is to export logs through command-line:


click on 'View Logs' link, to find out your Log Group and Log Stream
install "awscli" and "jq"


Run substituting your log-group-name and -log-stream-name:

aws logs get-log-events --log-group-name /aws/codebuild/Dumper  \
    --log-stream-name 0bd74b8c-74b9-4f9b-b275-167b45901aa3 | \
    jq '.events[].message' -r | grep -v '^$'


This should give you the output, which you can include in the question.