Instead of Slack -> Mattermost or Rocket.Chat Sentry also has self-hosted option available (and it's also opensource). Instead of GitHub + Travis CI, you can

Instead of Slack -> Mattermost or Rocket.Chat Sentry also has self-hosted option available (and it's also opensource). Instead of GitHub + Travis CI, you can use GitLab (it also has bundled CI capability, based on Docker). with GitLab, you can also have Continuos Deployment, wired up with the CI solution. The best experience will be deploying to Kubernetes, as it will give you even monitoring, automatically, but you can code custom deployment logic as a step in the CI pipeline.