My current project makes use of the MySQL database, which runs in a Docker container.
At a certain moment connecting to the database became excruciatingly slow, taking tens of seconds to establish a single connection. After that everything would work as expected.
The application opens a connection some hundred times, so the startup time had become really unacceptable.
I've spent a lot of time hunting that down, and then even more time looking for a solution as I failed to find any on StackOverflow. But finally I've solved this.
The culprit was, as I initially thought, the DNS lookup: the database was trying to determine the name of the host that was connecting to it, and the DNS was slow. But in my use case it was a pretty useless operation.
First I tried to pass the
--dns=127.0.0.1 to Docker, but it wouldn't improve the situation.
What did help was MySQL's flag
--skip-name-resolve: the issue disappeared and making a connection takes milliseconds now.
A container can be started with something like:
docker run -e MYSQL_ROOT_PASSWORD=secret mysql:5.7.16 --skip-name-resolve
I hope it helps someone struggling with the same issue.