psycopg2 on elastic beanstalk - can't deploy app

I solved it, you need to open you EC2 instance first, then install like this

sudo yum install postgresql-devel

Then deploy your EB

Funny enough, the solution for me for Amazon Linux 2 ended up being what the original question was - adding a 01_package.conf with the contents of

packages:
  yum:
    postgresql-devel: []

Furthmore, this was contrary to almost all answers I found online which directed to use postgresql96-devel or some other number. I found out I needed to make the package name postgresql-devel after SSHing onto the EC2 instance and viewing all available Yum packages.

[ec2-user@ip-xxx-xxx-xxx-xxx ~]$ yum list available | grep 'postgresql'
freeradius-postgresql.x86_64           3.0.13-10.amzn2                amzn2-core
pcp-pmda-postgresql.x86_64             3.12.2-5.amzn2                 amzn2-core
postgresql.x86_64                      10.4-5.amzn2.0.2               amzn2extra-postgresql10
postgresql-contrib.x86_64              10.4-5.amzn2.0.2               amzn2extra-postgresql10
postgresql-devel.x86_64                10.4-5.amzn2.0.2               @amzn2extra-postgresql10
postgresql-docs.x86_64                 10.4-5.amzn2.0.2               amzn2extra-postgresql10
...

and I saw it was just postgres-devel. Once I changed it to that it deployed alright. Make sure you commit your change if you're using eb with git before running eb deploy - or at least add the changes to your git staging area and run with eb deploy --staged as well. That one cost me a run around thinking I had already tried the package name when I hadn't

I found the answers on this stackoverflow post here to be helpful as well. Good luck!

---

I ended up needing a newer psql client (11.x) than what was default using the above answer (9.2 at the time of posting). This answer here was the only way I could make it work. Answer pasted here for posterity...

packages:
    yum:
        amazon-linux-extras: []

commands:
    01_postgres_activate:
        command: sudo amazon-linux-extras enable postgresql11
    02_postgres_install:
        command: sudo yum install -y postgresql-devel

Even after installing postgresql93-devel, I kept getting an error "no module named psycopg2". To solve this I had to connect to my enviroment with eb ssh and then execute sudo pip install psycopg2 to solve this.